feat(security): implement OAuth2 authorization server with database support

- Add OAuthServer for handling OAuth2 flows including authorization, token exchange, and client registration.
- Introduce DatabaseAuthenticator for persisting clients and authorization codes.
- Implement SQL procedures for client registration, code saving, and token introspection.
- Support for external OAuth2 providers and PKCE (Proof Key for Code Exchange).

pkg/dbmanager/providers/postgres_listener_example_test.go

@@ -3,6 +3,7 @@ package providers_test
 import (
 	"context"
 	"fmt"
+	"log"
 	"time"
 
 	"github.com/bitechdev/ResolveSpec/pkg/dbmanager"
@@ -29,14 +30,14 @@ func ExamplePostgresListener_basic() {
 	ctx := context.Background()
 
 	if err := provider.Connect(ctx, cfg); err != nil {
-		panic(fmt.Sprintf("Failed to connect: %v", err))
+		log.Fatalf("Failed to connect: %v", err)
 	}
 	defer provider.Close()
 
 	// Get listener
 	listener, err := provider.GetListener(ctx)
 	if err != nil {
-		panic(fmt.Sprintf("Failed to get listener: %v", err))
+		log.Fatalf("Failed to get listener: %v", err)
 	}
 
 	// Subscribe to a channel with a handler
@@ -44,13 +45,13 @@ func ExamplePostgresListener_basic() {
 		fmt.Printf("Received notification on %s: %s\n", channel, payload)
 	})
 	if err != nil {
-		panic(fmt.Sprintf("Failed to listen: %v", err))
+		log.Fatalf("Failed to listen: %v", err)
 	}
 
 	// Send a notification
 	err = listener.Notify(ctx, "user_events", `{"event":"user_created","user_id":123}`)
 	if err != nil {
-		panic(fmt.Sprintf("Failed to notify: %v", err))
+		log.Fatalf("Failed to notify: %v", err)
 	}
 
 	// Wait for notification to be processed
@@ -58,7 +59,7 @@ func ExamplePostgresListener_basic() {
 
 	// Unsubscribe from the channel
 	if err := listener.Unlisten("user_events"); err != nil {
-		panic(fmt.Sprintf("Failed to unlisten: %v", err))
+		log.Fatalf("Failed to unlisten: %v", err)
 	}
 }
 
@@ -80,13 +81,13 @@ func ExamplePostgresListener_multipleChannels() {
 	ctx := context.Background()
 
 	if err := provider.Connect(ctx, cfg); err != nil {
-		panic(fmt.Sprintf("Failed to connect: %v", err))
+		log.Fatalf("Failed to connect: %v", err)
 	}
 	defer provider.Close()
 
 	listener, err := provider.GetListener(ctx)
 	if err != nil {
-		panic(fmt.Sprintf("Failed to get listener: %v", err))
+		log.Fatalf("Failed to get listener: %v", err)
 	}
 
 	// Listen to multiple channels
@@ -97,7 +98,7 @@ func ExamplePostgresListener_multipleChannels() {
 			fmt.Printf("[%s] %s\n", ch, payload)
 		})
 		if err != nil {
-			panic(fmt.Sprintf("Failed to listen on %s: %v", channel, err))
+			log.Fatalf("Failed to listen on %s: %v", channel, err)
 		}
 	}
 
@@ -140,14 +141,14 @@ func ExamplePostgresListener_withDBManager() {
 
 	provider := providers.NewPostgresProvider()
 	if err := provider.Connect(ctx, cfg); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 	defer provider.Close()
 
 	// Get listener
 	listener, err := provider.GetListener(ctx)
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Subscribe to application events
@@ -186,13 +187,13 @@ func ExamplePostgresListener_errorHandling() {
 	ctx := context.Background()
 
 	if err := provider.Connect(ctx, cfg); err != nil {
-		panic(fmt.Sprintf("Failed to connect: %v", err))
+		log.Fatalf("Failed to connect: %v", err)
 	}
 	defer provider.Close()
 
 	listener, err := provider.GetListener(ctx)
 	if err != nil {
-		panic(fmt.Sprintf("Failed to get listener: %v", err))
+		log.Fatalf("Failed to get listener: %v", err)
 	}
 
 	// The listener automatically reconnects if the connection is lost

pkg/resolvemcp/README.md

@@ -142,9 +142,137 @@ e.Any("/mcp", echo.WrapHandler(h))     // Echo
 
 ---
 
-### Authentication
+## OAuth2 Authentication
 
-Add middleware before the MCP routes. The handler itself has no auth layer.
+`resolvemcp` ships a full **MCP-standard OAuth2 authorization server** (`pkg/security.OAuthServer`) that MCP clients (Claude Desktop, Cursor, etc.) can discover and use automatically.
+
+It can operate as:
+- **Its own identity provider** — shows a login form, validates via `DatabaseAuthenticator.Login()`
+- **An OAuth2 federation layer** — delegates to external providers (Google, GitHub, Microsoft, etc.)
+- **Both simultaneously**
+
+### Standard endpoints served
+
+| Path | Spec | Purpose |
+|---|---|---|
+| `GET /.well-known/oauth-authorization-server` | RFC 8414 | MCP client auto-discovery |
+| `POST /oauth/register` | RFC 7591 | Dynamic client registration |
+| `GET /oauth/authorize` | OAuth 2.1 + PKCE | Start login (form or provider redirect) |
+| `POST /oauth/authorize` | — | Login form submission |
+| `POST /oauth/token` | OAuth 2.1 | Auth code → Bearer token exchange |
+| `POST /oauth/token` (refresh) | OAuth 2.1 | Refresh token rotation |
+| `GET /oauth/provider/callback` | Internal | External provider redirect target |
+
+MCP clients send `Authorization: Bearer <token>` on all subsequent requests.
+
+---
+
+### Mode 1 — Direct login (server as identity provider)
+
+```go
+import "github.com/bitechdev/ResolveSpec/pkg/security"
+
+db, _ := sql.Open("postgres", dsn)
+auth := security.NewDatabaseAuthenticator(db)
+
+handler := resolvemcp.NewHandlerWithGORM(gormDB, resolvemcp.Config{
+    BaseURL:  "https://api.example.com",
+    BasePath: "/mcp",
+})
+
+// Enable the OAuth2 server — auth enables the login form
+handler.EnableOAuthServer(security.OAuthServerConfig{
+    Issuer: "https://api.example.com",
+}, auth)
+
+provider, _ := security.NewCompositeSecurityProvider(auth, colSec, rowSec)
+securityList, _ := security.NewSecurityList(provider)
+security.RegisterSecurityHooks(handler, securityList)
+
+http.ListenAndServe(":8080", handler.HTTPHandler(securityList))
+```
+
+MCP client flow:
+1. Discovers server at `/.well-known/oauth-authorization-server`
+2. Registers itself at `/oauth/register`
+3. Redirects user to `/oauth/authorize` → login form appears
+4. On submit, exchanges code at `/oauth/token` → receives `Authorization: Bearer` token
+5. Uses token on all MCP tool calls
+
+---
+
+### Mode 2 — External provider (Google, GitHub, etc.)
+
+The `RedirectURL` in the provider config must point to `/oauth/provider/callback` on this server.
+
+```go
+auth := security.NewDatabaseAuthenticator(db).WithOAuth2(security.OAuth2Config{
+    ClientID:     os.Getenv("GOOGLE_CLIENT_ID"),
+    ClientSecret: os.Getenv("GOOGLE_CLIENT_SECRET"),
+    RedirectURL:  "https://api.example.com/oauth/provider/callback",
+    Scopes:       []string{"openid", "profile", "email"},
+    AuthURL:      "https://accounts.google.com/o/oauth2/auth",
+    TokenURL:     "https://oauth2.googleapis.com/token",
+    UserInfoURL:  "https://www.googleapis.com/oauth2/v2/userinfo",
+    ProviderName: "google",
+})
+
+// nil = no password login; Google handles auth
+handler.EnableOAuthServer(security.OAuthServerConfig{
+    Issuer: "https://api.example.com",
+}, nil)
+handler.RegisterOAuth2Provider(auth, "google")
+```
+
+---
+
+### Mode 3 — Both (login form + external providers)
+
+```go
+handler.EnableOAuthServer(security.OAuthServerConfig{
+    Issuer:     "https://api.example.com",
+    LoginTitle: "My App Login",
+}, auth) // auth enables the username/password form
+
+handler.RegisterOAuth2Provider(googleAuth, "google")
+handler.RegisterOAuth2Provider(githubAuth, "github")
+```
+
+When external providers are registered they take priority; the login form is used as fallback when no providers are configured.
+
+---
+
+### Using `security.OAuthServer` standalone
+
+The authorization server lives in `pkg/security` and can be used with any HTTP framework independently of `resolvemcp`:
+
+```go
+oauthSrv := security.NewOAuthServer(security.OAuthServerConfig{
+    Issuer: "https://api.example.com",
+}, auth)
+oauthSrv.RegisterExternalProvider(googleAuth, "google")
+
+mux := http.NewServeMux()
+mux.Handle("/", oauthSrv.HTTPHandler())   // mounts all OAuth2 routes
+mux.Handle("/mcp/", myMCPHandler)
+http.ListenAndServe(":8080", mux)
+```
+
+---
+
+### Cookie-based flow (legacy)
+
+For simple setups without full MCP OAuth2 compliance, use the legacy helpers that set a session cookie after external provider login:
+
+```go
+resolvemcp.SetupMuxOAuth2Routes(r, auth, resolvemcp.OAuth2RouteConfig{
+    ProviderName:       "google",
+    LoginPath:          "/auth/google/login",
+    CallbackPath:       "/auth/google/callback",
+    AfterLoginRedirect: "/",
+})
+resolvemcp.SetupMuxRoutesWithAuth(r, handler, securityList)
+```
 
 ---
 

pkg/resolvemcp/handler.go

@@ -16,17 +16,20 @@ import (
 	"github.com/bitechdev/ResolveSpec/pkg/logger"
 	"github.com/bitechdev/ResolveSpec/pkg/modelregistry"
 	"github.com/bitechdev/ResolveSpec/pkg/reflection"
+	"github.com/bitechdev/ResolveSpec/pkg/security"
 )
 
 // Handler exposes registered database models as MCP tools and resources.
 type Handler struct {
-	db        common.Database
+	db         common.Database
-	registry  common.ModelRegistry
+	registry   common.ModelRegistry
-	hooks     *HookRegistry
+	hooks      *HookRegistry
-	mcpServer *server.MCPServer
+	mcpServer  *server.MCPServer
-	config    Config
+	config     Config
-	name      string
+	name       string
-	version   string
+	version    string
+	oauth2Regs []oauth2Registration
+	oauthSrv   *security.OAuthServer
 }
 
 // NewHandler creates a Handler with the given database, model registry, and config.
@@ -197,8 +200,19 @@ func (h *Handler) getSchemaAndTable(defaultSchema, entity string, model interfac
 	return defaultSchema, entity
 }
 
+// recoverPanic catches a panic from the current goroutine and returns it as an error.
+// Usage: defer recoverPanic(&returnedErr)
+func recoverPanic(err *error) {
+	if r := recover(); r != nil {
+		msg := fmt.Sprintf("%v", r)
+		logger.Error("[resolvemcp] panic recovered: %s", msg)
+		*err = fmt.Errorf("internal error: %s", msg)
+	}
+}
+
 // executeRead reads records from the database and returns raw data + metadata.
-func (h *Handler) executeRead(ctx context.Context, schema, entity, id string, options common.RequestOptions) (interface{}, *common.Metadata, error) {
+func (h *Handler) executeRead(ctx context.Context, schema, entity, id string, options common.RequestOptions) (_ interface{}, _ *common.Metadata, retErr error) {
+	defer recoverPanic(&retErr)
 	model, err := h.registry.GetModelByEntity(schema, entity)
 	if err != nil {
 		return nil, nil, fmt.Errorf("model not found: %w", err)
@@ -254,15 +268,6 @@ func (h *Handler) executeRead(ctx context.Context, schema, entity, id string, op
 		query = query.ColumnExpr(fmt.Sprintf("(%s) AS %s", cu.Expression, cu.Name))
 	}
 
-	// Preloads
-	if len(options.Preload) > 0 {
-		var err error
-		query, err = h.applyPreloads(model, query, options.Preload)
-		if err != nil {
-			return nil, nil, fmt.Errorf("failed to apply preloads: %w", err)
-		}
-	}
-
 	// Filters
 	query = h.applyFilters(query, options.Filters)
 
@@ -304,7 +309,7 @@ func (h *Handler) executeRead(ctx context.Context, schema, entity, id string, op
 		}
 	}
 
-	// Count
+	// Count — must happen before preloads are applied; Bun panics when counting with relations.
 	total, err := query.Count(ctx)
 	if err != nil {
 		return nil, nil, fmt.Errorf("error counting records: %w", err)
@@ -318,6 +323,15 @@ func (h *Handler) executeRead(ctx context.Context, schema, entity, id string, op
 		query = query.Offset(*options.Offset)
 	}
 
+	// Preloads — applied after count to avoid Bun panic when counting with relations.
+	if len(options.Preload) > 0 {
+		var preloadErr error
+		query, preloadErr = h.applyPreloads(model, query, options.Preload)
+		if preloadErr != nil {
+			return nil, nil, fmt.Errorf("failed to apply preloads: %w", preloadErr)
+		}
+	}
+
 	// BeforeRead hook
 	hookCtx.Query = query
 	if err := h.hooks.Execute(BeforeRead, hookCtx); err != nil {
@@ -378,7 +392,8 @@ func (h *Handler) executeRead(ctx context.Context, schema, entity, id string, op
 }
 
 // executeCreate inserts one or more records.
-func (h *Handler) executeCreate(ctx context.Context, schema, entity string, data interface{}) (interface{}, error) {
+func (h *Handler) executeCreate(ctx context.Context, schema, entity string, data interface{}) (_ interface{}, retErr error) {
+	defer recoverPanic(&retErr)
 	model, err := h.registry.GetModelByEntity(schema, entity)
 	if err != nil {
 		return nil, fmt.Errorf("model not found: %w", err)
@@ -462,7 +477,8 @@ func (h *Handler) executeCreate(ctx context.Context, schema, entity string, data
 }
 
 // executeUpdate updates a record by ID.
-func (h *Handler) executeUpdate(ctx context.Context, schema, entity, id string, data interface{}) (interface{}, error) {
+func (h *Handler) executeUpdate(ctx context.Context, schema, entity, id string, data interface{}) (_ interface{}, retErr error) {
+	defer recoverPanic(&retErr)
 	model, err := h.registry.GetModelByEntity(schema, entity)
 	if err != nil {
 		return nil, fmt.Errorf("model not found: %w", err)
@@ -572,7 +588,8 @@ func (h *Handler) executeUpdate(ctx context.Context, schema, entity, id string,
 }
 
 // executeDelete deletes a record by ID.
-func (h *Handler) executeDelete(ctx context.Context, schema, entity, id string) (interface{}, error) {
+func (h *Handler) executeDelete(ctx context.Context, schema, entity, id string) (_ interface{}, retErr error) {
+	defer recoverPanic(&retErr)
 	if id == "" {
 		return nil, fmt.Errorf("delete requires an ID")
 	}

pkg/resolvemcp/oauth2.go

@@ -0,0 +1,264 @@
+package resolvemcp
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/gorilla/mux"
+
+	"github.com/bitechdev/ResolveSpec/pkg/security"
+)
+
+// --------------------------------------------------------------------------
+// OAuth2 registration on the Handler
+// --------------------------------------------------------------------------
+
+// oauth2Registration stores a configured auth provider and its route config.
+type oauth2Registration struct {
+	auth *security.DatabaseAuthenticator
+	cfg  OAuth2RouteConfig
+}
+
+// RegisterOAuth2 attaches an OAuth2 provider to the Handler.
+// The login and callback HTTP routes are served by HTTPHandler / StreamableHTTPMux.
+// Call this once per provider before serving requests.
+//
+// Example:
+//
+//	auth := security.NewGoogleAuthenticator(clientID, secret, redirectURL, db)
+//	handler.RegisterOAuth2(auth, resolvemcp.OAuth2RouteConfig{
+//	    ProviderName:       "google",
+//	    LoginPath:          "/auth/google/login",
+//	    CallbackPath:       "/auth/google/callback",
+//	    AfterLoginRedirect: "/",
+//	})
+func (h *Handler) RegisterOAuth2(auth *security.DatabaseAuthenticator, cfg OAuth2RouteConfig) {
+	h.oauth2Regs = append(h.oauth2Regs, oauth2Registration{auth: auth, cfg: cfg})
+}
+
+// HTTPHandler returns a single http.Handler that serves:
+//   - MCP OAuth2 authorization server endpoints (when EnableOAuthServer has been called)
+//   - OAuth2 login + callback routes for every registered provider (legacy cookie flow)
+//   - The MCP SSE transport wrapped with required authentication middleware
+//
+// Example:
+//
+//	auth := security.NewGoogleAuthenticator(...)
+//	handler.RegisterOAuth2(auth, cfg)
+//	handler.EnableOAuthServer(resolvemcp.OAuthServerConfig{Issuer: "https://api.example.com"})
+//	security.RegisterSecurityHooks(handler, securityList)
+//	http.ListenAndServe(":8080", handler.HTTPHandler(securityList))
+func (h *Handler) HTTPHandler(securityList *security.SecurityList) http.Handler {
+	mux := http.NewServeMux()
+	if h.oauthSrv != nil {
+		h.mountOAuthServerRoutes(mux)
+	}
+	h.mountOAuth2Routes(mux)
+
+	mcpHandler := h.AuthedSSEServer(securityList)
+	basePath := h.config.BasePath
+	if basePath == "" {
+		basePath = "/mcp"
+	}
+	mux.Handle(basePath+"/sse", mcpHandler)
+	mux.Handle(basePath+"/message", mcpHandler)
+	mux.Handle(basePath+"/", http.StripPrefix(basePath, mcpHandler))
+
+	return mux
+}
+
+// StreamableHTTPMux returns a single http.Handler that serves:
+//   - MCP OAuth2 authorization server endpoints (when EnableOAuthServer has been called)
+//   - OAuth2 login + callback routes for every registered provider (legacy cookie flow)
+//   - The MCP streamable HTTP transport wrapped with required authentication middleware
+//
+// Example:
+//
+//	http.ListenAndServe(":8080", handler.StreamableHTTPMux(securityList))
+func (h *Handler) StreamableHTTPMux(securityList *security.SecurityList) http.Handler {
+	mux := http.NewServeMux()
+	if h.oauthSrv != nil {
+		h.mountOAuthServerRoutes(mux)
+	}
+	h.mountOAuth2Routes(mux)
+
+	mcpHandler := h.AuthedStreamableHTTPServer(securityList)
+	basePath := h.config.BasePath
+	if basePath == "" {
+		basePath = "/mcp"
+	}
+	mux.Handle(basePath+"/", http.StripPrefix(basePath, mcpHandler))
+	mux.Handle(basePath, mcpHandler)
+
+	return mux
+}
+
+// mountOAuth2Routes registers all stored OAuth2 login+callback routes onto mux.
+func (h *Handler) mountOAuth2Routes(mux *http.ServeMux) {
+	for _, reg := range h.oauth2Regs {
+		var cookieOpts []security.SessionCookieOptions
+		if reg.cfg.CookieOptions != nil {
+			cookieOpts = append(cookieOpts, *reg.cfg.CookieOptions)
+		}
+		mux.Handle(reg.cfg.LoginPath, OAuth2LoginHandler(reg.auth, reg.cfg.ProviderName))
+		mux.Handle(reg.cfg.CallbackPath, OAuth2CallbackHandler(reg.auth, reg.cfg.ProviderName, reg.cfg.AfterLoginRedirect, cookieOpts...))
+	}
+}
+
+// --------------------------------------------------------------------------
+// Auth-wrapped transports
+// --------------------------------------------------------------------------
+
+// AuthedSSEServer wraps SSEServer with required authentication middleware from pkg/security.
+// The middleware reads the session cookie / Authorization header and populates the user
+// context into the request context, making it available to BeforeHandle security hooks.
+// Unauthenticated requests receive 401 before reaching any MCP tool.
+func (h *Handler) AuthedSSEServer(securityList *security.SecurityList) http.Handler {
+	return security.NewAuthMiddleware(securityList)(h.SSEServer())
+}
+
+// OptionalAuthSSEServer wraps SSEServer with optional authentication middleware.
+// Unauthenticated requests continue as guest rather than returning 401.
+// Use together with RegisterSecurityHooks and per-model CanPublicRead/Write rules
+// to allow mixed public/private access.
+func (h *Handler) OptionalAuthSSEServer(securityList *security.SecurityList) http.Handler {
+	return security.NewOptionalAuthMiddleware(securityList)(h.SSEServer())
+}
+
+// AuthedStreamableHTTPServer wraps StreamableHTTPServer with required authentication middleware.
+func (h *Handler) AuthedStreamableHTTPServer(securityList *security.SecurityList) http.Handler {
+	return security.NewAuthMiddleware(securityList)(h.StreamableHTTPServer())
+}
+
+// OptionalAuthStreamableHTTPServer wraps StreamableHTTPServer with optional authentication middleware.
+func (h *Handler) OptionalAuthStreamableHTTPServer(securityList *security.SecurityList) http.Handler {
+	return security.NewOptionalAuthMiddleware(securityList)(h.StreamableHTTPServer())
+}
+
+// --------------------------------------------------------------------------
+// OAuth2 route config and standalone handlers
+// --------------------------------------------------------------------------
+
+// OAuth2RouteConfig configures the OAuth2 HTTP endpoints for a single provider.
+type OAuth2RouteConfig struct {
+	// ProviderName is the OAuth2 provider name as registered with WithOAuth2()
+	// (e.g. "google", "github", "microsoft").
+	ProviderName string
+
+	// LoginPath is the HTTP path that redirects the browser to the OAuth2 provider
+	// (e.g. "/auth/google/login").
+	LoginPath string
+
+	// CallbackPath is the HTTP path that the OAuth2 provider redirects back to
+	// (e.g. "/auth/google/callback"). Must match the RedirectURL in OAuth2Config.
+	CallbackPath string
+
+	// AfterLoginRedirect is the URL to redirect the browser to after a successful
+	// login. When empty the LoginResponse JSON is written directly to the response.
+	AfterLoginRedirect string
+
+	// CookieOptions customises the session cookie written on successful login.
+	// Defaults to HttpOnly, Secure, SameSite=Lax when nil.
+	CookieOptions *security.SessionCookieOptions
+}
+
+// OAuth2LoginHandler returns an http.HandlerFunc that redirects the browser to
+// the OAuth2 provider's authorization URL.
+//
+// Register it on any router:
+//
+//	mux.Handle("/auth/google/login", resolvemcp.OAuth2LoginHandler(auth, "google"))
+func OAuth2LoginHandler(auth *security.DatabaseAuthenticator, providerName string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		state, err := auth.OAuth2GenerateState()
+		if err != nil {
+			http.Error(w, "failed to generate state", http.StatusInternalServerError)
+			return
+		}
+		authURL, err := auth.OAuth2GetAuthURL(providerName, state)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		http.Redirect(w, r, authURL, http.StatusTemporaryRedirect)
+	}
+}
+
+// OAuth2CallbackHandler returns an http.HandlerFunc that handles the OAuth2 provider
+// callback: exchanges the authorization code for a session token, writes the session
+// cookie, then either redirects to afterLoginRedirect or writes the LoginResponse as JSON.
+//
+// Register it on any router:
+//
+//	mux.Handle("/auth/google/callback", resolvemcp.OAuth2CallbackHandler(auth, "google", "/dashboard"))
+func OAuth2CallbackHandler(auth *security.DatabaseAuthenticator, providerName, afterLoginRedirect string, cookieOpts ...security.SessionCookieOptions) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		code := r.URL.Query().Get("code")
+		state := r.URL.Query().Get("state")
+		if code == "" {
+			http.Error(w, "missing code parameter", http.StatusBadRequest)
+			return
+		}
+
+		loginResp, err := auth.OAuth2HandleCallback(r.Context(), providerName, code, state)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusUnauthorized)
+			return
+		}
+
+		security.SetSessionCookie(w, loginResp, cookieOpts...)
+
+		if afterLoginRedirect != "" {
+			http.Redirect(w, r, afterLoginRedirect, http.StatusTemporaryRedirect)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(loginResp) //nolint:errcheck
+	}
+}
+
+// --------------------------------------------------------------------------
+// Gorilla Mux convenience helpers
+// --------------------------------------------------------------------------
+
+// SetupMuxOAuth2Routes registers the OAuth2 login and callback routes on a Gorilla Mux router.
+//
+// Example:
+//
+//	resolvemcp.SetupMuxOAuth2Routes(r, auth, resolvemcp.OAuth2RouteConfig{
+//	    ProviderName: "google", LoginPath: "/auth/google/login",
+//	    CallbackPath: "/auth/google/callback", AfterLoginRedirect: "/",
+//	})
+func SetupMuxOAuth2Routes(muxRouter *mux.Router, auth *security.DatabaseAuthenticator, cfg OAuth2RouteConfig) {
+	var cookieOpts []security.SessionCookieOptions
+	if cfg.CookieOptions != nil {
+		cookieOpts = append(cookieOpts, *cfg.CookieOptions)
+	}
+
+	muxRouter.Handle(cfg.LoginPath,
+		OAuth2LoginHandler(auth, cfg.ProviderName),
+	).Methods(http.MethodGet)
+
+	muxRouter.Handle(cfg.CallbackPath,
+		OAuth2CallbackHandler(auth, cfg.ProviderName, cfg.AfterLoginRedirect, cookieOpts...),
+	).Methods(http.MethodGet)
+}
+
+// SetupMuxRoutesWithAuth mounts the MCP SSE endpoints on a Gorilla Mux router
+// with required authentication middleware applied.
+func SetupMuxRoutesWithAuth(muxRouter *mux.Router, handler *Handler, securityList *security.SecurityList) {
+	basePath := handler.config.BasePath
+	h := handler.AuthedSSEServer(securityList)
+
+	muxRouter.Handle(basePath+"/sse", h).Methods(http.MethodGet, http.MethodOptions)
+	muxRouter.Handle(basePath+"/message", h).Methods(http.MethodPost, http.MethodOptions)
+	muxRouter.PathPrefix(basePath).Handler(http.StripPrefix(basePath, h))
+}
+
+// SetupMuxStreamableHTTPRoutesWithAuth mounts the MCP streamable HTTP endpoint on a
+// Gorilla Mux router with required authentication middleware applied.
+func SetupMuxStreamableHTTPRoutesWithAuth(muxRouter *mux.Router, handler *Handler, securityList *security.SecurityList) {
+	basePath := handler.config.BasePath
+	h := handler.AuthedStreamableHTTPServer(securityList)
+	muxRouter.PathPrefix(basePath).Handler(http.StripPrefix(basePath, h))
+}

pkg/resolvemcp/oauth2_server.go

@@ -0,0 +1,51 @@
+package resolvemcp
+
+import (
+	"net/http"
+
+	"github.com/bitechdev/ResolveSpec/pkg/security"
+)
+
+// EnableOAuthServer activates the MCP-standard OAuth2 authorization server on this Handler.
+//
+// Pass a DatabaseAuthenticator to enable direct username/password login — the server acts as
+// its own identity provider and renders a login form at /oauth/authorize. Pass nil to use
+// only external providers registered via RegisterOAuth2Provider.
+//
+// After calling this, HTTPHandler and StreamableHTTPMux serve the full set of RFC-compliant
+// endpoints required by MCP clients alongside the MCP transport:
+//
+//	GET  /.well-known/oauth-authorization-server   RFC 8414 — auto-discovery
+//	POST /oauth/register                            RFC 7591 — dynamic client registration
+//	GET  /oauth/authorize                           OAuth 2.1 + PKCE — start login
+//	POST /oauth/authorize                           Login form submission (password flow)
+//	POST /oauth/token                               Bearer token exchange + refresh
+//	GET  /oauth/provider/callback                   External provider redirect target
+func (h *Handler) EnableOAuthServer(cfg security.OAuthServerConfig, auth *security.DatabaseAuthenticator) {
+	h.oauthSrv = security.NewOAuthServer(cfg, auth)
+	// Wire any external providers already registered via RegisterOAuth2
+	for _, reg := range h.oauth2Regs {
+		h.oauthSrv.RegisterExternalProvider(reg.auth, reg.cfg.ProviderName)
+	}
+}
+
+// RegisterOAuth2Provider adds an external OAuth2 provider to the MCP OAuth2 authorization server.
+// EnableOAuthServer must be called before this. The auth must have been configured with
+// WithOAuth2(providerName, ...) for the given provider name.
+func (h *Handler) RegisterOAuth2Provider(auth *security.DatabaseAuthenticator, providerName string) {
+	if h.oauthSrv != nil {
+		h.oauthSrv.RegisterExternalProvider(auth, providerName)
+	}
+}
+
+// mountOAuthServerRoutes mounts the security.OAuthServer's HTTP handler onto mux.
+func (h *Handler) mountOAuthServerRoutes(mux *http.ServeMux) {
+	oauthHandler := h.oauthSrv.HTTPHandler()
+	// Delegate all /oauth/ and /.well-known/ paths to the OAuth server
+	mux.Handle("/.well-known/", oauthHandler)
+	mux.Handle("/oauth/", oauthHandler)
+	if h.oauthSrv != nil {
+		// Also mount the external provider callback path if it differs from /oauth/
+		mux.Handle(h.oauthSrv.ProviderCallbackPath(), oauthHandler)
+	}
+}

pkg/security/README.md

@@ -12,6 +12,7 @@ Type-safe, composable security system for ResolveSpec with support for authentic
 - ✅ **Testable** - Easy to mock and test
 - ✅ **Extensible** - Implement custom providers for your needs
 - ✅ **Stored Procedures** - All database operations use PostgreSQL stored procedures for security and maintainability
+- ✅ **OAuth2 Authorization Server** - Built-in OAuth 2.1 + PKCE server (RFC 8414, 7591, 7009, 7662) with login form and external provider federation
 
 ## Stored Procedure Architecture
 
@@ -38,6 +39,12 @@ Type-safe, composable security system for ResolveSpec with support for authentic
 | `resolvespec_jwt_logout` | JWT token blacklist | JWTAuthenticator |
 | `resolvespec_column_security` | Load column rules | DatabaseColumnSecurityProvider |
 | `resolvespec_row_security` | Load row templates | DatabaseRowSecurityProvider |
+| `resolvespec_oauth_register_client` | Persist OAuth2 client (RFC 7591) | OAuthServer / DatabaseAuthenticator |
+| `resolvespec_oauth_get_client` | Retrieve OAuth2 client by ID | OAuthServer / DatabaseAuthenticator |
+| `resolvespec_oauth_save_code` | Persist authorization code | OAuthServer / DatabaseAuthenticator |
+| `resolvespec_oauth_exchange_code` | Consume authorization code (single-use) | OAuthServer / DatabaseAuthenticator |
+| `resolvespec_oauth_introspect` | Token introspection (RFC 7662) | OAuthServer / DatabaseAuthenticator |
+| `resolvespec_oauth_revoke` | Token revocation (RFC 7009) | OAuthServer / DatabaseAuthenticator |
 
 See `database_schema.sql` for complete stored procedure definitions and examples.
 
@@ -897,6 +904,155 @@ securityList := security.NewSecurityList(provider)
 restheadspec.RegisterSecurityHooks(handler, securityList) // or funcspec/resolvespec
 ```
 
+## OAuth2 Authorization Server
+
+`OAuthServer` is a generic OAuth 2.1 + PKCE authorization server. It is not tied to any spec — `pkg/resolvemcp` uses it, but it can be used standalone with any `http.ServeMux`.
+
+### Endpoints
+
+| Method | Path | RFC |
+|--------|------|-----|
+| `GET` | `/.well-known/oauth-authorization-server` | RFC 8414 — server metadata |
+| `POST` | `/oauth/register` | RFC 7591 — dynamic client registration |
+| `GET` | `/oauth/authorize` | OAuth 2.1 — start authorization / provider selection |
+| `POST` | `/oauth/authorize` | OAuth 2.1 — login form submission |
+| `POST` | `/oauth/token` | OAuth 2.1 — code exchange + refresh |
+| `POST` | `/oauth/revoke` | RFC 7009 — token revocation |
+| `POST` | `/oauth/introspect` | RFC 7662 — token introspection |
+| `GET` | `{ProviderCallbackPath}` | External provider redirect target |
+
+### Config
+
+```go
+cfg := security.OAuthServerConfig{
+    Issuer:               "https://example.com",      // Required — token issuer URL
+    ProviderCallbackPath: "/oauth/provider/callback", // External provider redirect target
+    LoginTitle:           "My App Login",             // HTML login page title
+    PersistClients:       true,  // Store clients in DB (multi-instance safe)
+    PersistCodes:         true,  // Store codes in DB (multi-instance safe)
+    DefaultScopes:        []string{"openid", "profile"}, // Returned when no scope requested
+    AccessTokenTTL:       time.Hour,
+    AuthCodeTTL:          5 * time.Minute,
+}
+```
+
+| Field | Default | Notes |
+|-------|---------|-------|
+| `Issuer` | — | Required |
+| `ProviderCallbackPath` | `/oauth/provider/callback` | |
+| `LoginTitle` | `"Login"` | |
+| `PersistClients` | `false` | Set `true` for multi-instance |
+| `PersistCodes` | `false` | Set `true` for multi-instance |
+| `DefaultScopes` | `nil` | |
+| `AccessTokenTTL` | `1h` | |
+| `AuthCodeTTL` | `5m` | |
+
+### Operating Modes
+
+**Mode 1 — Direct login (username/password form)**
+
+Pass a `*DatabaseAuthenticator` to `NewOAuthServer`. The server renders a login form at `GET /oauth/authorize` and issues tokens via the stored session after login.
+
+```go
+auth := security.NewDatabaseAuthenticator(db)
+srv := security.NewOAuthServer(cfg, auth)
+```
+
+**Mode 2 — External provider federation**
+
+Pass `nil` as auth and register external providers. The authorize page shows a provider selection UI.
+
+```go
+srv := security.NewOAuthServer(cfg, nil)
+srv.RegisterExternalProvider(googleAuth, "google")
+srv.RegisterExternalProvider(githubAuth, "github")
+```
+
+**Mode 3 — Both**
+
+Pass auth for the login form and also register external providers. The authorize page shows both a login form and provider buttons.
+
+```go
+srv := security.NewOAuthServer(cfg, auth)
+srv.RegisterExternalProvider(googleAuth, "google")
+```
+
+### Standalone Usage
+
+```go
+mux := http.NewServeMux()
+mux.Handle("/.well-known/", srv.HTTPHandler())
+mux.Handle("/oauth/", srv.HTTPHandler())
+mux.Handle(cfg.ProviderCallbackPath, srv.HTTPHandler())
+
+http.ListenAndServe(":8080", mux)
+```
+
+### DB Persistence
+
+When `PersistClients: true` or `PersistCodes: true`, the server calls the corresponding `DatabaseAuthenticator` methods. Both flags default to `false` (in-memory maps). Enable both for multi-instance deployments.
+
+Requires `oauth_clients` and `oauth_codes` tables + 6 stored procedures from `database_schema.sql`.
+
+#### New DB Types
+
+```go
+type OAuthServerClient struct {
+    ClientID      string   `json:"client_id"`
+    RedirectURIs  []string `json:"redirect_uris"`
+    ClientName    string   `json:"client_name,omitempty"`
+    GrantTypes    []string `json:"grant_types"`
+    AllowedScopes []string `json:"allowed_scopes,omitempty"`
+}
+
+type OAuthCode struct {
+    Code                string    `json:"code"`
+    ClientID            string    `json:"client_id"`
+    RedirectURI         string    `json:"redirect_uri"`
+    ClientState         string    `json:"client_state,omitempty"`
+    CodeChallenge       string    `json:"code_challenge"`
+    CodeChallengeMethod string    `json:"code_challenge_method"`
+    SessionToken        string    `json:"session_token"`
+    Scopes              []string  `json:"scopes,omitempty"`
+    ExpiresAt           time.Time `json:"expires_at"`
+}
+
+type OAuthTokenInfo struct {
+    Active   bool     `json:"active"`
+    Sub      string   `json:"sub,omitempty"`
+    Username string   `json:"username,omitempty"`
+    Email    string   `json:"email,omitempty"`
+    Roles    []string `json:"roles,omitempty"`
+    Exp      int64    `json:"exp,omitempty"`
+    Iat      int64    `json:"iat,omitempty"`
+}
+```
+
+#### DatabaseAuthenticator OAuth Methods
+
+```go
+auth.OAuthRegisterClient(ctx, client)  // RFC 7591 — persist client
+auth.OAuthGetClient(ctx, clientID)     // retrieve client
+auth.OAuthSaveCode(ctx, code)          // persist authorization code
+auth.OAuthExchangeCode(ctx, code)      // consume code (single-use, deletes on read)
+auth.OAuthIntrospectToken(ctx, token)  // RFC 7662 — returns OAuthTokenInfo
+auth.OAuthRevokeToken(ctx, token)      // RFC 7009 — revoke session
+```
+
+#### SQLNames Fields
+
+```go
+type SQLNames struct {
+    // ... existing fields ...
+    OAuthRegisterClient string // default: "resolvespec_oauth_register_client"
+    OAuthGetClient      string // default: "resolvespec_oauth_get_client"
+    OAuthSaveCode       string // default: "resolvespec_oauth_save_code"
+    OAuthExchangeCode   string // default: "resolvespec_oauth_exchange_code"
+    OAuthIntrospect     string // default: "resolvespec_oauth_introspect"
+    OAuthRevoke         string // default: "resolvespec_oauth_revoke"
+}
+```
+
 The main changes:
 1. Security package no longer knows about specific spec types
 2. Each spec registers its own security hooks

pkg/security/database_schema.sql

@@ -1397,3 +1397,173 @@ $$ LANGUAGE plpgsql;
 
 -- Get credentials by username
 -- SELECT * FROM resolvespec_passkey_get_credentials_by_username('admin');
+
+-- ============================================
+-- OAuth2 Server Tables (OAuthServer persistence)
+-- ============================================
+
+-- oauth_clients: persistent RFC 7591 registered clients
+CREATE TABLE IF NOT EXISTS oauth_clients (
+    id SERIAL PRIMARY KEY,
+    client_id VARCHAR(255) NOT NULL UNIQUE,
+    redirect_uris TEXT[] NOT NULL,
+    client_name VARCHAR(255),
+    grant_types TEXT[] DEFAULT ARRAY['authorization_code'],
+    allowed_scopes TEXT[] DEFAULT ARRAY['openid','profile','email'],
+    is_active BOOLEAN DEFAULT true,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- oauth_codes: short-lived authorization codes (for multi-instance deployments)
+CREATE TABLE IF NOT EXISTS oauth_codes (
+    id SERIAL PRIMARY KEY,
+    code VARCHAR(255) NOT NULL UNIQUE,
+    client_id VARCHAR(255) NOT NULL REFERENCES oauth_clients(client_id) ON DELETE CASCADE,
+    redirect_uri TEXT NOT NULL,
+    client_state TEXT,
+    code_challenge VARCHAR(255) NOT NULL,
+    code_challenge_method VARCHAR(10) DEFAULT 'S256',
+    session_token TEXT NOT NULL,
+    scopes TEXT[],
+    expires_at TIMESTAMP NOT NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+CREATE INDEX IF NOT EXISTS idx_oauth_codes_code ON oauth_codes(code);
+CREATE INDEX IF NOT EXISTS idx_oauth_codes_expires ON oauth_codes(expires_at);
+
+-- ============================================
+-- OAuth2 Server Stored Procedures
+-- ============================================
+
+CREATE OR REPLACE FUNCTION resolvespec_oauth_register_client(p_data jsonb)
+RETURNS TABLE(p_success bool, p_error text, p_data jsonb)
+LANGUAGE plpgsql AS $$
+DECLARE
+    v_client_id   text;
+    v_row         jsonb;
+BEGIN
+    v_client_id := p_data->>'client_id';
+
+    INSERT INTO oauth_clients (client_id, redirect_uris, client_name, grant_types, allowed_scopes)
+    VALUES (
+        v_client_id,
+        ARRAY(SELECT jsonb_array_elements_text(p_data->'redirect_uris')),
+        p_data->>'client_name',
+        COALESCE(ARRAY(SELECT jsonb_array_elements_text(p_data->'grant_types')), ARRAY['authorization_code']),
+        COALESCE(ARRAY(SELECT jsonb_array_elements_text(p_data->'allowed_scopes')), ARRAY['openid','profile','email'])
+    )
+    RETURNING to_jsonb(oauth_clients.*) INTO v_row;
+
+    RETURN QUERY SELECT true, null::text, v_row;
+EXCEPTION WHEN OTHERS THEN
+    RETURN QUERY SELECT false, SQLERRM, null::jsonb;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION resolvespec_oauth_get_client(p_client_id text)
+RETURNS TABLE(p_success bool, p_error text, p_data jsonb)
+LANGUAGE plpgsql AS $$
+DECLARE
+    v_row jsonb;
+BEGIN
+    SELECT to_jsonb(oauth_clients.*)
+    INTO v_row
+    FROM oauth_clients
+    WHERE client_id = p_client_id AND is_active = true;
+
+    IF v_row IS NULL THEN
+        RETURN QUERY SELECT false, 'client not found'::text, null::jsonb;
+    ELSE
+        RETURN QUERY SELECT true, null::text, v_row;
+    END IF;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION resolvespec_oauth_save_code(p_data jsonb)
+RETURNS TABLE(p_success bool, p_error text)
+LANGUAGE plpgsql AS $$
+BEGIN
+    INSERT INTO oauth_codes (code, client_id, redirect_uri, client_state, code_challenge, code_challenge_method, session_token, scopes, expires_at)
+    VALUES (
+        p_data->>'code',
+        p_data->>'client_id',
+        p_data->>'redirect_uri',
+        p_data->>'client_state',
+        p_data->>'code_challenge',
+        COALESCE(p_data->>'code_challenge_method', 'S256'),
+        p_data->>'session_token',
+        ARRAY(SELECT jsonb_array_elements_text(p_data->'scopes')),
+        (p_data->>'expires_at')::timestamp
+    );
+
+    RETURN QUERY SELECT true, null::text;
+EXCEPTION WHEN OTHERS THEN
+    RETURN QUERY SELECT false, SQLERRM;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION resolvespec_oauth_exchange_code(p_code text)
+RETURNS TABLE(p_success bool, p_error text, p_data jsonb)
+LANGUAGE plpgsql AS $$
+DECLARE
+    v_row jsonb;
+BEGIN
+    DELETE FROM oauth_codes
+    WHERE code = p_code AND expires_at > now()
+    RETURNING jsonb_build_object(
+        'client_id',             client_id,
+        'redirect_uri',          redirect_uri,
+        'client_state',          client_state,
+        'code_challenge',        code_challenge,
+        'code_challenge_method', code_challenge_method,
+        'session_token',         session_token,
+        'scopes',                to_jsonb(scopes)
+    ) INTO v_row;
+
+    IF v_row IS NULL THEN
+        RETURN QUERY SELECT false, 'invalid or expired code'::text, null::jsonb;
+    ELSE
+        RETURN QUERY SELECT true, null::text, v_row;
+    END IF;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION resolvespec_oauth_introspect(p_token text)
+RETURNS TABLE(p_success bool, p_error text, p_data jsonb)
+LANGUAGE plpgsql AS $$
+DECLARE
+    v_row jsonb;
+BEGIN
+    SELECT jsonb_build_object(
+        'active',     true,
+        'sub',        u.id::text,
+        'username',   u.username,
+        'email',      u.email,
+        'user_level', u.user_level,
+        'roles',      to_jsonb(string_to_array(COALESCE(u.roles, ''), ',')),
+        'exp',        EXTRACT(EPOCH FROM s.expires_at)::bigint,
+        'iat',        EXTRACT(EPOCH FROM s.created_at)::bigint
+    )
+    INTO v_row
+    FROM user_sessions s
+    JOIN users u ON u.id = s.user_id
+    WHERE s.session_token = p_token
+      AND s.expires_at > now()
+      AND u.is_active = true;
+
+    IF v_row IS NULL THEN
+        RETURN QUERY SELECT true, null::text, '{"active":false}'::jsonb;
+    ELSE
+        RETURN QUERY SELECT true, null::text, v_row;
+    END IF;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION resolvespec_oauth_revoke(p_token text)
+RETURNS TABLE(p_success bool, p_error text)
+LANGUAGE plpgsql AS $$
+BEGIN
+    DELETE FROM user_sessions WHERE session_token = p_token;
+    RETURN QUERY SELECT true, null::text;
+END;
+$$;

pkg/security/oauth_server.go

@@ -0,0 +1,859 @@
+package security
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+)
+
+// OAuthServerConfig configures the MCP-standard OAuth2 authorization server.
+type OAuthServerConfig struct {
+	// Issuer is the public base URL of this server (e.g. "https://api.example.com").
+	// Used in /.well-known/oauth-authorization-server and to build endpoint URLs.
+	Issuer string
+
+	// ProviderCallbackPath is the path on this server that external OAuth2 providers
+	// redirect back to. Defaults to "/oauth/provider/callback".
+	ProviderCallbackPath string
+
+	// LoginTitle is shown on the built-in login form when the server acts as its own
+	// identity provider. Defaults to "MCP Login".
+	LoginTitle string
+
+	// PersistClients stores registered clients in the database when a DatabaseAuthenticator is provided.
+	// Clients registered during a session survive server restarts.
+	PersistClients bool
+
+	// PersistCodes stores authorization codes in the database.
+	// Useful for multi-instance deployments. Defaults to in-memory.
+	PersistCodes bool
+
+	// DefaultScopes lists scopes advertised in server metadata. Defaults to ["openid","profile","email"].
+	DefaultScopes []string
+
+	// AccessTokenTTL is the issued token lifetime. Defaults to 24h.
+	AccessTokenTTL time.Duration
+
+	// AuthCodeTTL is the auth code lifetime. Defaults to 2 minutes.
+	AuthCodeTTL time.Duration
+}
+
+// oauthClient is a dynamically registered OAuth2 client (RFC 7591).
+type oauthClient struct {
+	ClientID      string   `json:"client_id"`
+	RedirectURIs  []string `json:"redirect_uris"`
+	ClientName    string   `json:"client_name,omitempty"`
+	GrantTypes    []string `json:"grant_types"`
+	AllowedScopes []string `json:"allowed_scopes,omitempty"`
+}
+
+// pendingAuth tracks an in-progress authorization code exchange.
+type pendingAuth struct {
+	ClientID            string
+	RedirectURI         string
+	ClientState         string
+	CodeChallenge       string
+	CodeChallengeMethod string
+	ProviderName        string // empty = password login
+	ExpiresAt           time.Time
+	SessionToken        string   // set after authentication completes
+	Scopes              []string // requested scopes
+}
+
+// externalProvider pairs a DatabaseAuthenticator with its provider name.
+type externalProvider struct {
+	auth         *DatabaseAuthenticator
+	providerName string
+}
+
+// OAuthServer implements the MCP-standard OAuth2 authorization server (OAuth 2.1 + PKCE).
+//
+// It can act as both:
+//   - A direct identity provider using DatabaseAuthenticator username/password login
+//   - A federation layer that delegates authentication to external OAuth2 providers
+//     (Google, GitHub, Microsoft, etc.) registered via RegisterExternalProvider
+//
+// The server exposes these RFC-compliant endpoints:
+//
+//	GET  /.well-known/oauth-authorization-server   RFC 8414 — server metadata discovery
+//	POST /oauth/register                            RFC 7591 — dynamic client registration
+//	GET  /oauth/authorize                           OAuth 2.1 + PKCE — start authorization
+//	POST /oauth/authorize                           Direct login form submission
+//	POST /oauth/token                               Token exchange and refresh
+//	POST /oauth/revoke                              RFC 7009 — token revocation
+//	POST /oauth/introspect                          RFC 7662 — token introspection
+//	GET  {ProviderCallbackPath}                     Internal — external provider callback
+type OAuthServer struct {
+	cfg       OAuthServerConfig
+	auth      *DatabaseAuthenticator // nil = only external providers
+	providers []externalProvider
+
+	mu      sync.RWMutex
+	clients map[string]*oauthClient
+	pending map[string]*pendingAuth // provider_state → pending (external flow)
+	codes   map[string]*pendingAuth // auth_code     → pending (post-auth)
+}
+
+// NewOAuthServer creates a new MCP OAuth2 authorization server.
+//
+// Pass a DatabaseAuthenticator to enable direct username/password login (the server
+// acts as its own identity provider). Pass nil to use only external providers.
+// External providers are added separately via RegisterExternalProvider.
+func NewOAuthServer(cfg OAuthServerConfig, auth *DatabaseAuthenticator) *OAuthServer {
+	if cfg.ProviderCallbackPath == "" {
+		cfg.ProviderCallbackPath = "/oauth/provider/callback"
+	}
+	if cfg.LoginTitle == "" {
+		cfg.LoginTitle = "Sign in"
+	}
+	if len(cfg.DefaultScopes) == 0 {
+		cfg.DefaultScopes = []string{"openid", "profile", "email"}
+	}
+	if cfg.AccessTokenTTL == 0 {
+		cfg.AccessTokenTTL = 24 * time.Hour
+	}
+	if cfg.AuthCodeTTL == 0 {
+		cfg.AuthCodeTTL = 2 * time.Minute
+	}
+	s := &OAuthServer{
+		cfg:     cfg,
+		auth:    auth,
+		clients: make(map[string]*oauthClient),
+		pending: make(map[string]*pendingAuth),
+		codes:   make(map[string]*pendingAuth),
+	}
+	go s.cleanupExpired()
+	return s
+}
+
+// RegisterExternalProvider adds an external OAuth2 provider (Google, GitHub, Microsoft, etc.)
+// that handles user authentication via redirect. The DatabaseAuthenticator must have been
+// configured with WithOAuth2(providerName, ...) before calling this.
+// Multiple providers can be registered; the first is used as the default.
+func (s *OAuthServer) RegisterExternalProvider(auth *DatabaseAuthenticator, providerName string) {
+	s.providers = append(s.providers, externalProvider{auth: auth, providerName: providerName})
+}
+
+// ProviderCallbackPath returns the configured path for external provider callbacks.
+func (s *OAuthServer) ProviderCallbackPath() string {
+	return s.cfg.ProviderCallbackPath
+}
+
+// HTTPHandler returns an http.Handler that serves all RFC-required OAuth2 endpoints.
+// Mount it at the root of your HTTP server alongside the MCP transport.
+//
+//	mux := http.NewServeMux()
+//	mux.Handle("/", oauthServer.HTTPHandler())
+//	mux.Handle("/mcp/", mcpTransport)
+func (s *OAuthServer) HTTPHandler() http.Handler {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/.well-known/oauth-authorization-server", s.metadataHandler)
+	mux.HandleFunc("/oauth/register", s.registerHandler)
+	mux.HandleFunc("/oauth/authorize", s.authorizeHandler)
+	mux.HandleFunc("/oauth/token", s.tokenHandler)
+	mux.HandleFunc("/oauth/revoke", s.revokeHandler)
+	mux.HandleFunc("/oauth/introspect", s.introspectHandler)
+	mux.HandleFunc(s.cfg.ProviderCallbackPath, s.providerCallbackHandler)
+	return mux
+}
+
+// cleanupExpired removes stale pending auths and codes every 5 minutes.
+func (s *OAuthServer) cleanupExpired() {
+	ticker := time.NewTicker(5 * time.Minute)
+	defer ticker.Stop()
+	for range ticker.C {
+		now := time.Now()
+		s.mu.Lock()
+		for k, p := range s.pending {
+			if now.After(p.ExpiresAt) {
+				delete(s.pending, k)
+			}
+		}
+		for k, p := range s.codes {
+			if now.After(p.ExpiresAt) {
+				delete(s.codes, k)
+			}
+		}
+		s.mu.Unlock()
+	}
+}
+
+// --------------------------------------------------------------------------
+// RFC 8414 — Server metadata
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) metadataHandler(w http.ResponseWriter, r *http.Request) {
+	issuer := s.cfg.Issuer
+	meta := map[string]interface{}{
+		"issuer":                                issuer,
+		"authorization_endpoint":                issuer + "/oauth/authorize",
+		"token_endpoint":                        issuer + "/oauth/token",
+		"registration_endpoint":                 issuer + "/oauth/register",
+		"revocation_endpoint":                   issuer + "/oauth/revoke",
+		"introspection_endpoint":                issuer + "/oauth/introspect",
+		"scopes_supported":                      s.cfg.DefaultScopes,
+		"response_types_supported":              []string{"code"},
+		"grant_types_supported":                 []string{"authorization_code", "refresh_token"},
+		"code_challenge_methods_supported":      []string{"S256"},
+		"token_endpoint_auth_methods_supported": []string{"none"},
+	}
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(meta) //nolint:errcheck
+}
+
+// --------------------------------------------------------------------------
+// RFC 7591 — Dynamic client registration
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) registerHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	var req struct {
+		RedirectURIs  []string `json:"redirect_uris"`
+		ClientName    string   `json:"client_name"`
+		GrantTypes    []string `json:"grant_types"`
+		AllowedScopes []string `json:"allowed_scopes"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeOAuthError(w, "invalid_request", "malformed JSON", http.StatusBadRequest)
+		return
+	}
+	if len(req.RedirectURIs) == 0 {
+		writeOAuthError(w, "invalid_request", "redirect_uris required", http.StatusBadRequest)
+		return
+	}
+	grantTypes := req.GrantTypes
+	if len(grantTypes) == 0 {
+		grantTypes = []string{"authorization_code"}
+	}
+	allowedScopes := req.AllowedScopes
+	if len(allowedScopes) == 0 {
+		allowedScopes = s.cfg.DefaultScopes
+	}
+	clientID, err := randomOAuthToken()
+	if err != nil {
+		http.Error(w, "server error", http.StatusInternalServerError)
+		return
+	}
+	client := &oauthClient{
+		ClientID:      clientID,
+		RedirectURIs:  req.RedirectURIs,
+		ClientName:    req.ClientName,
+		GrantTypes:    grantTypes,
+		AllowedScopes: allowedScopes,
+	}
+
+	if s.cfg.PersistClients && s.auth != nil {
+		dbClient := &OAuthServerClient{
+			ClientID:      client.ClientID,
+			RedirectURIs:  client.RedirectURIs,
+			ClientName:    client.ClientName,
+			GrantTypes:    client.GrantTypes,
+			AllowedScopes: client.AllowedScopes,
+		}
+		if _, err := s.auth.OAuthRegisterClient(r.Context(), dbClient); err != nil {
+			http.Error(w, "server error", http.StatusInternalServerError)
+			return
+		}
+	}
+
+	s.mu.Lock()
+	s.clients[clientID] = client
+	s.mu.Unlock()
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusCreated)
+	json.NewEncoder(w).Encode(client) //nolint:errcheck
+}
+
+// --------------------------------------------------------------------------
+// Authorization endpoint — GET + POST /oauth/authorize
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) authorizeHandler(w http.ResponseWriter, r *http.Request) {
+	switch r.Method {
+	case http.MethodGet:
+		s.authorizeGet(w, r)
+	case http.MethodPost:
+		s.authorizePost(w, r)
+	default:
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+	}
+}
+
+// authorizeGet validates the request and either:
+//   - Redirects to an external provider (if providers are registered)
+//   - Renders a login form (if the server is its own identity provider)
+func (s *OAuthServer) authorizeGet(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query()
+	clientID := q.Get("client_id")
+	redirectURI := q.Get("redirect_uri")
+	clientState := q.Get("state")
+	codeChallenge := q.Get("code_challenge")
+	codeChallengeMethod := q.Get("code_challenge_method")
+	providerName := q.Get("provider")
+	scopeStr := q.Get("scope")
+	var scopes []string
+	if scopeStr != "" {
+		scopes = strings.Fields(scopeStr)
+	}
+
+	if q.Get("response_type") != "code" {
+		writeOAuthError(w, "unsupported_response_type", "only 'code' is supported", http.StatusBadRequest)
+		return
+	}
+	if codeChallenge == "" {
+		writeOAuthError(w, "invalid_request", "code_challenge required (PKCE S256)", http.StatusBadRequest)
+		return
+	}
+	if codeChallengeMethod != "" && codeChallengeMethod != "S256" {
+		writeOAuthError(w, "invalid_request", "only S256 code_challenge_method is supported", http.StatusBadRequest)
+		return
+	}
+	client, ok := s.lookupOrFetchClient(r.Context(), clientID)
+	if !ok {
+		writeOAuthError(w, "invalid_client", "unknown client_id", http.StatusBadRequest)
+		return
+	}
+	if !oauthSliceContains(client.RedirectURIs, redirectURI) {
+		writeOAuthError(w, "invalid_request", "redirect_uri not registered", http.StatusBadRequest)
+		return
+	}
+
+	// External provider path
+	if len(s.providers) > 0 {
+		s.redirectToExternalProvider(w, r, clientID, redirectURI, clientState, codeChallenge, codeChallengeMethod, providerName, scopes)
+		return
+	}
+
+	// Direct login form path (server is its own identity provider)
+	if s.auth == nil {
+		http.Error(w, "no authentication provider configured", http.StatusInternalServerError)
+		return
+	}
+	s.renderLoginForm(w, r, clientID, redirectURI, clientState, codeChallenge, codeChallengeMethod, scopeStr, "")
+}
+
+// authorizePost handles login form submission for the direct login flow.
+func (s *OAuthServer) authorizePost(w http.ResponseWriter, r *http.Request) {
+	if err := r.ParseForm(); err != nil {
+		http.Error(w, "invalid form", http.StatusBadRequest)
+		return
+	}
+
+	clientID := r.FormValue("client_id")
+	redirectURI := r.FormValue("redirect_uri")
+	clientState := r.FormValue("client_state")
+	codeChallenge := r.FormValue("code_challenge")
+	codeChallengeMethod := r.FormValue("code_challenge_method")
+	username := r.FormValue("username")
+	password := r.FormValue("password")
+	scopeStr := r.FormValue("scope")
+	var scopes []string
+	if scopeStr != "" {
+		scopes = strings.Fields(scopeStr)
+	}
+
+	client, ok := s.lookupOrFetchClient(r.Context(), clientID)
+	if !ok || !oauthSliceContains(client.RedirectURIs, redirectURI) {
+		http.Error(w, "invalid client or redirect_uri", http.StatusBadRequest)
+		return
+	}
+	if s.auth == nil {
+		http.Error(w, "no authentication provider configured", http.StatusInternalServerError)
+		return
+	}
+
+	loginResp, err := s.auth.Login(r.Context(), LoginRequest{
+		Username: username,
+		Password: password,
+	})
+	if err != nil {
+		s.renderLoginForm(w, r, clientID, redirectURI, clientState, codeChallenge, codeChallengeMethod, scopeStr, "Invalid username or password")
+		return
+	}
+
+	s.issueCodeAndRedirect(w, r, loginResp.Token, clientID, redirectURI, clientState, codeChallenge, codeChallengeMethod, "", scopes)
+}
+
+// redirectToExternalProvider stores the pending auth and redirects to the configured provider.
+func (s *OAuthServer) redirectToExternalProvider(w http.ResponseWriter, r *http.Request, clientID, redirectURI, clientState, codeChallenge, codeChallengeMethod, providerName string, scopes []string) {
+	var provider *externalProvider
+	if providerName != "" {
+		for i := range s.providers {
+			if s.providers[i].providerName == providerName {
+				provider = &s.providers[i]
+				break
+			}
+		}
+		if provider == nil {
+			http.Error(w, fmt.Sprintf("provider %q not found", providerName), http.StatusBadRequest)
+			return
+		}
+	} else {
+		provider = &s.providers[0]
+	}
+
+	providerState, err := randomOAuthToken()
+	if err != nil {
+		http.Error(w, "server error", http.StatusInternalServerError)
+		return
+	}
+
+	pending := &pendingAuth{
+		ClientID:            clientID,
+		RedirectURI:         redirectURI,
+		ClientState:         clientState,
+		CodeChallenge:       codeChallenge,
+		CodeChallengeMethod: codeChallengeMethod,
+		ProviderName:        provider.providerName,
+		ExpiresAt:           time.Now().Add(10 * time.Minute),
+		Scopes:              scopes,
+	}
+	s.mu.Lock()
+	s.pending[providerState] = pending
+	s.mu.Unlock()
+
+	authURL, err := provider.auth.OAuth2GetAuthURL(provider.providerName, providerState)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(w, r, authURL, http.StatusFound)
+}
+
+// --------------------------------------------------------------------------
+// External provider callback — GET {ProviderCallbackPath}
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) providerCallbackHandler(w http.ResponseWriter, r *http.Request) {
+	code := r.URL.Query().Get("code")
+	providerState := r.URL.Query().Get("state")
+
+	if code == "" {
+		http.Error(w, "missing code", http.StatusBadRequest)
+		return
+	}
+
+	s.mu.Lock()
+	pending, ok := s.pending[providerState]
+	if ok {
+		delete(s.pending, providerState)
+	}
+	s.mu.Unlock()
+
+	if !ok || time.Now().After(pending.ExpiresAt) {
+		http.Error(w, "invalid or expired state", http.StatusBadRequest)
+		return
+	}
+
+	provider := s.providerByName(pending.ProviderName)
+	if provider == nil {
+		http.Error(w, fmt.Sprintf("provider %q not found", pending.ProviderName), http.StatusInternalServerError)
+		return
+	}
+
+	loginResp, err := provider.auth.OAuth2HandleCallback(r.Context(), pending.ProviderName, code, providerState)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusUnauthorized)
+		return
+	}
+
+	s.issueCodeAndRedirect(w, r, loginResp.Token,
+		pending.ClientID, pending.RedirectURI, pending.ClientState,
+		pending.CodeChallenge, pending.CodeChallengeMethod, pending.ProviderName, pending.Scopes)
+}
+
+// issueCodeAndRedirect generates a short-lived auth code and redirects to the MCP client.
+func (s *OAuthServer) issueCodeAndRedirect(w http.ResponseWriter, r *http.Request, sessionToken, clientID, redirectURI, clientState, codeChallenge, codeChallengeMethod, providerName string, scopes []string) {
+	authCode, err := randomOAuthToken()
+	if err != nil {
+		http.Error(w, "server error", http.StatusInternalServerError)
+		return
+	}
+
+	pending := &pendingAuth{
+		ClientID:            clientID,
+		RedirectURI:         redirectURI,
+		ClientState:         clientState,
+		CodeChallenge:       codeChallenge,
+		CodeChallengeMethod: codeChallengeMethod,
+		ProviderName:        providerName,
+		SessionToken:        sessionToken,
+		ExpiresAt:           time.Now().Add(s.cfg.AuthCodeTTL),
+		Scopes:              scopes,
+	}
+
+	if s.cfg.PersistCodes && s.auth != nil {
+		oauthCode := &OAuthCode{
+			Code:                authCode,
+			ClientID:            clientID,
+			RedirectURI:         redirectURI,
+			ClientState:         clientState,
+			CodeChallenge:       codeChallenge,
+			CodeChallengeMethod: codeChallengeMethod,
+			SessionToken:        sessionToken,
+			Scopes:              scopes,
+			ExpiresAt:           pending.ExpiresAt,
+		}
+		if err := s.auth.OAuthSaveCode(r.Context(), oauthCode); err != nil {
+			http.Error(w, "server error", http.StatusInternalServerError)
+			return
+		}
+	} else {
+		s.mu.Lock()
+		s.codes[authCode] = pending
+		s.mu.Unlock()
+	}
+
+	redirectURL, err := url.Parse(redirectURI)
+	if err != nil {
+		http.Error(w, "invalid redirect_uri", http.StatusInternalServerError)
+		return
+	}
+	qp := redirectURL.Query()
+	qp.Set("code", authCode)
+	if clientState != "" {
+		qp.Set("state", clientState)
+	}
+	redirectURL.RawQuery = qp.Encode()
+	http.Redirect(w, r, redirectURL.String(), http.StatusFound)
+}
+
+// --------------------------------------------------------------------------
+// Token endpoint — POST /oauth/token
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) tokenHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	if err := r.ParseForm(); err != nil {
+		writeOAuthError(w, "invalid_request", "cannot parse form", http.StatusBadRequest)
+		return
+	}
+	switch r.FormValue("grant_type") {
+	case "authorization_code":
+		s.handleAuthCodeGrant(w, r)
+	case "refresh_token":
+		s.handleRefreshGrant(w, r)
+	default:
+		writeOAuthError(w, "unsupported_grant_type", "", http.StatusBadRequest)
+	}
+}
+
+func (s *OAuthServer) handleAuthCodeGrant(w http.ResponseWriter, r *http.Request) {
+	code := r.FormValue("code")
+	redirectURI := r.FormValue("redirect_uri")
+	clientID := r.FormValue("client_id")
+	codeVerifier := r.FormValue("code_verifier")
+
+	if code == "" || codeVerifier == "" {
+		writeOAuthError(w, "invalid_request", "code and code_verifier required", http.StatusBadRequest)
+		return
+	}
+
+	var sessionToken string
+	var scopes []string
+
+	if s.cfg.PersistCodes && s.auth != nil {
+		oauthCode, err := s.auth.OAuthExchangeCode(r.Context(), code)
+		if err != nil {
+			writeOAuthError(w, "invalid_grant", "code expired or invalid", http.StatusBadRequest)
+			return
+		}
+		if oauthCode.ClientID != clientID {
+			writeOAuthError(w, "invalid_client", "", http.StatusBadRequest)
+			return
+		}
+		if oauthCode.RedirectURI != redirectURI {
+			writeOAuthError(w, "invalid_grant", "redirect_uri mismatch", http.StatusBadRequest)
+			return
+		}
+		if !validatePKCESHA256(oauthCode.CodeChallenge, codeVerifier) {
+			writeOAuthError(w, "invalid_grant", "code_verifier invalid", http.StatusBadRequest)
+			return
+		}
+		sessionToken = oauthCode.SessionToken
+		scopes = oauthCode.Scopes
+	} else {
+		s.mu.Lock()
+		pending, ok := s.codes[code]
+		if ok {
+			delete(s.codes, code)
+		}
+		s.mu.Unlock()
+
+		if !ok || time.Now().After(pending.ExpiresAt) {
+			writeOAuthError(w, "invalid_grant", "code expired or invalid", http.StatusBadRequest)
+			return
+		}
+		if pending.ClientID != clientID {
+			writeOAuthError(w, "invalid_client", "", http.StatusBadRequest)
+			return
+		}
+		if pending.RedirectURI != redirectURI {
+			writeOAuthError(w, "invalid_grant", "redirect_uri mismatch", http.StatusBadRequest)
+			return
+		}
+		if !validatePKCESHA256(pending.CodeChallenge, codeVerifier) {
+			writeOAuthError(w, "invalid_grant", "code_verifier invalid", http.StatusBadRequest)
+			return
+		}
+		sessionToken = pending.SessionToken
+		scopes = pending.Scopes
+	}
+
+	writeOAuthToken(w, sessionToken, "", scopes)
+}
+
+func (s *OAuthServer) handleRefreshGrant(w http.ResponseWriter, r *http.Request) {
+	refreshToken := r.FormValue("refresh_token")
+	providerName := r.FormValue("provider")
+	if refreshToken == "" {
+		writeOAuthError(w, "invalid_request", "refresh_token required", http.StatusBadRequest)
+		return
+	}
+
+	// Try external providers first, then fall back to DatabaseAuthenticator
+	provider := s.providerByName(providerName)
+	if provider != nil {
+		loginResp, err := provider.auth.OAuth2RefreshToken(r.Context(), refreshToken, providerName)
+		if err != nil {
+			writeOAuthError(w, "invalid_grant", err.Error(), http.StatusBadRequest)
+			return
+		}
+		writeOAuthToken(w, loginResp.Token, loginResp.RefreshToken, nil)
+		return
+	}
+
+	if s.auth != nil {
+		loginResp, err := s.auth.RefreshToken(r.Context(), refreshToken)
+		if err != nil {
+			writeOAuthError(w, "invalid_grant", err.Error(), http.StatusBadRequest)
+			return
+		}
+		writeOAuthToken(w, loginResp.Token, loginResp.RefreshToken, nil)
+		return
+	}
+
+	writeOAuthError(w, "invalid_grant", "no provider available for refresh", http.StatusBadRequest)
+}
+
+// --------------------------------------------------------------------------
+// RFC 7009 — Token revocation
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) revokeHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	if err := r.ParseForm(); err != nil {
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+	token := r.FormValue("token")
+	if token == "" {
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+
+	if s.auth != nil {
+		s.auth.OAuthRevokeToken(r.Context(), token) //nolint:errcheck
+	}
+	w.WriteHeader(http.StatusOK)
+}
+
+// --------------------------------------------------------------------------
+// RFC 7662 — Token introspection
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) introspectHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	if err := r.ParseForm(); err != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{"active":false}`)) //nolint:errcheck
+		return
+	}
+	token := r.FormValue("token")
+	w.Header().Set("Content-Type", "application/json")
+
+	if token == "" || s.auth == nil {
+		w.Write([]byte(`{"active":false}`)) //nolint:errcheck
+		return
+	}
+
+	info, err := s.auth.OAuthIntrospectToken(r.Context(), token)
+	if err != nil {
+		w.Write([]byte(`{"active":false}`)) //nolint:errcheck
+		return
+	}
+	json.NewEncoder(w).Encode(info) //nolint:errcheck
+}
+
+// --------------------------------------------------------------------------
+// Login form (direct identity provider mode)
+// --------------------------------------------------------------------------
+
+func (s *OAuthServer) renderLoginForm(w http.ResponseWriter, r *http.Request, clientID, redirectURI, clientState, codeChallenge, codeChallengeMethod, scope, errMsg string) {
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	errHTML := ""
+	if errMsg != "" {
+		errHTML = `<p style="color:red">` + errMsg + `</p>`
+	}
+	fmt.Fprintf(w, loginFormHTML,
+		s.cfg.LoginTitle,
+		s.cfg.LoginTitle,
+		errHTML,
+		clientID,
+		htmlEscape(redirectURI),
+		htmlEscape(clientState),
+		htmlEscape(codeChallenge),
+		htmlEscape(codeChallengeMethod),
+		htmlEscape(scope),
+	)
+}
+
+const loginFormHTML = `<!DOCTYPE html>
+<html><head><meta charset="utf-8"><title>%s</title>
+<style>body{font-family:sans-serif;display:flex;justify-content:center;align-items:center;min-height:100vh;margin:0;background:#f5f5f5}
+.card{background:#fff;padding:2rem;border-radius:8px;box-shadow:0 2px 8px rgba(0,0,0,.15);width:320px}
+h2{margin:0 0 1.5rem;font-size:1.25rem}
+label{display:block;margin-bottom:.25rem;font-size:.875rem;color:#555}
+input[type=text],input[type=password]{width:100%%;box-sizing:border-box;padding:.5rem;border:1px solid #ccc;border-radius:4px;margin-bottom:1rem;font-size:1rem}
+button{width:100%%;padding:.6rem;background:#0070f3;color:#fff;border:none;border-radius:4px;font-size:1rem;cursor:pointer}
+button:hover{background:#005fd4}.err{color:#d32f2f;margin-bottom:1rem;font-size:.875rem}</style>
+</head><body><div class="card">
+<h2>%s</h2>%s
+<form method="POST" action="/oauth/authorize">
+<input type="hidden" name="client_id" value="%s">
+<input type="hidden" name="redirect_uri" value="%s">
+<input type="hidden" name="client_state" value="%s">
+<input type="hidden" name="code_challenge" value="%s">
+<input type="hidden" name="code_challenge_method" value="%s">
+<input type="hidden" name="scope" value="%s">
+<label>Username</label><input type="text" name="username" autofocus autocomplete="username">
+<label>Password</label><input type="password" name="password" autocomplete="current-password">
+<button type="submit">Sign in</button>
+</form></div></body></html>`
+
+// --------------------------------------------------------------------------
+// Helpers
+// --------------------------------------------------------------------------
+
+// lookupOrFetchClient checks in-memory first, then DB if PersistClients is enabled.
+func (s *OAuthServer) lookupOrFetchClient(ctx context.Context, clientID string) (*oauthClient, bool) {
+	s.mu.RLock()
+	c, ok := s.clients[clientID]
+	s.mu.RUnlock()
+	if ok {
+		return c, true
+	}
+
+	if !s.cfg.PersistClients || s.auth == nil {
+		return nil, false
+	}
+
+	dbClient, err := s.auth.OAuthGetClient(ctx, clientID)
+	if err != nil {
+		return nil, false
+	}
+
+	c = &oauthClient{
+		ClientID:      dbClient.ClientID,
+		RedirectURIs:  dbClient.RedirectURIs,
+		ClientName:    dbClient.ClientName,
+		GrantTypes:    dbClient.GrantTypes,
+		AllowedScopes: dbClient.AllowedScopes,
+	}
+	s.mu.Lock()
+	s.clients[clientID] = c
+	s.mu.Unlock()
+	return c, true
+}
+
+func (s *OAuthServer) providerByName(name string) *externalProvider {
+	for i := range s.providers {
+		if s.providers[i].providerName == name {
+			return &s.providers[i]
+		}
+	}
+	// If name is empty and only one provider exists, return it
+	if name == "" && len(s.providers) == 1 {
+		return &s.providers[0]
+	}
+	return nil
+}
+
+func validatePKCESHA256(challenge, verifier string) bool {
+	h := sha256.Sum256([]byte(verifier))
+	return base64.RawURLEncoding.EncodeToString(h[:]) == challenge
+}
+
+func randomOAuthToken() (string, error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}
+
+func oauthSliceContains(slice []string, s string) bool {
+	for _, v := range slice {
+		if strings.EqualFold(v, s) {
+			return true
+		}
+	}
+	return false
+}
+
+func writeOAuthToken(w http.ResponseWriter, accessToken, refreshToken string, scopes []string) {
+	resp := map[string]interface{}{
+		"access_token": accessToken,
+		"token_type":   "Bearer",
+		"expires_in":   86400,
+	}
+	if refreshToken != "" {
+		resp["refresh_token"] = refreshToken
+	}
+	if len(scopes) > 0 {
+		resp["scope"] = strings.Join(scopes, " ")
+	}
+	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Cache-Control", "no-store")
+	w.Header().Set("Pragma", "no-cache")
+	json.NewEncoder(w).Encode(resp) //nolint:errcheck
+}
+
+func writeOAuthError(w http.ResponseWriter, errCode, description string, status int) {
+	resp := map[string]string{"error": errCode}
+	if description != "" {
+		resp["error_description"] = description
+	}
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	json.NewEncoder(w).Encode(resp) //nolint:errcheck
+}
+
+func htmlEscape(s string) string {
+	s = strings.ReplaceAll(s, "&", "&amp;")
+	s = strings.ReplaceAll(s, `"`, "&#34;")
+	s = strings.ReplaceAll(s, "<", "&lt;")
+	s = strings.ReplaceAll(s, ">", "&gt;")
+	return s
+}

pkg/security/oauth_server_db.go

@@ -0,0 +1,202 @@
+package security
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+// OAuthServerClient is a persisted RFC 7591 registered OAuth2 client.
+type OAuthServerClient struct {
+	ClientID      string   `json:"client_id"`
+	RedirectURIs  []string `json:"redirect_uris"`
+	ClientName    string   `json:"client_name,omitempty"`
+	GrantTypes    []string `json:"grant_types"`
+	AllowedScopes []string `json:"allowed_scopes,omitempty"`
+}
+
+// OAuthCode is a short-lived authorization code.
+type OAuthCode struct {
+	Code                string    `json:"code"`
+	ClientID            string    `json:"client_id"`
+	RedirectURI         string    `json:"redirect_uri"`
+	ClientState         string    `json:"client_state,omitempty"`
+	CodeChallenge       string    `json:"code_challenge"`
+	CodeChallengeMethod string    `json:"code_challenge_method"`
+	SessionToken        string    `json:"session_token"`
+	Scopes              []string  `json:"scopes,omitempty"`
+	ExpiresAt           time.Time `json:"expires_at"`
+}
+
+// OAuthTokenInfo is the RFC 7662 token introspection response.
+type OAuthTokenInfo struct {
+	Active   bool     `json:"active"`
+	Sub      string   `json:"sub,omitempty"`
+	Username string   `json:"username,omitempty"`
+	Email    string   `json:"email,omitempty"`
+	Roles    []string `json:"roles,omitempty"`
+	Exp      int64    `json:"exp,omitempty"`
+	Iat      int64    `json:"iat,omitempty"`
+}
+
+// OAuthRegisterClient persists an OAuth2 client registration.
+func (a *DatabaseAuthenticator) OAuthRegisterClient(ctx context.Context, client *OAuthServerClient) (*OAuthServerClient, error) {
+	input, err := json.Marshal(client)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal client: %w", err)
+	}
+
+	var success bool
+	var errMsg *string
+	var data []byte
+
+	err = a.db.QueryRowContext(ctx, fmt.Sprintf(`
+		SELECT p_success, p_error, p_data::text
+		FROM %s($1::jsonb)
+	`, a.sqlNames.OAuthRegisterClient), input).Scan(&success, &errMsg, &data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to register client: %w", err)
+	}
+	if !success {
+		if errMsg != nil {
+			return nil, fmt.Errorf("%s", *errMsg)
+		}
+		return nil, fmt.Errorf("failed to register client")
+	}
+
+	var result OAuthServerClient
+	if err := json.Unmarshal(data, &result); err != nil {
+		return nil, fmt.Errorf("failed to parse registered client: %w", err)
+	}
+	return &result, nil
+}
+
+// OAuthGetClient retrieves a registered client by ID.
+func (a *DatabaseAuthenticator) OAuthGetClient(ctx context.Context, clientID string) (*OAuthServerClient, error) {
+	var success bool
+	var errMsg *string
+	var data []byte
+
+	err := a.db.QueryRowContext(ctx, fmt.Sprintf(`
+		SELECT p_success, p_error, p_data::text
+		FROM %s($1)
+	`, a.sqlNames.OAuthGetClient), clientID).Scan(&success, &errMsg, &data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get client: %w", err)
+	}
+	if !success {
+		if errMsg != nil {
+			return nil, fmt.Errorf("%s", *errMsg)
+		}
+		return nil, fmt.Errorf("client not found")
+	}
+
+	var result OAuthServerClient
+	if err := json.Unmarshal(data, &result); err != nil {
+		return nil, fmt.Errorf("failed to parse client: %w", err)
+	}
+	return &result, nil
+}
+
+// OAuthSaveCode persists an authorization code.
+func (a *DatabaseAuthenticator) OAuthSaveCode(ctx context.Context, code *OAuthCode) error {
+	input, err := json.Marshal(code)
+	if err != nil {
+		return fmt.Errorf("failed to marshal code: %w", err)
+	}
+
+	var success bool
+	var errMsg *string
+
+	err = a.db.QueryRowContext(ctx, fmt.Sprintf(`
+		SELECT p_success, p_error
+		FROM %s($1::jsonb)
+	`, a.sqlNames.OAuthSaveCode), input).Scan(&success, &errMsg)
+	if err != nil {
+		return fmt.Errorf("failed to save code: %w", err)
+	}
+	if !success {
+		if errMsg != nil {
+			return fmt.Errorf("%s", *errMsg)
+		}
+		return fmt.Errorf("failed to save code")
+	}
+	return nil
+}
+
+// OAuthExchangeCode retrieves and deletes an authorization code (single use).
+func (a *DatabaseAuthenticator) OAuthExchangeCode(ctx context.Context, code string) (*OAuthCode, error) {
+	var success bool
+	var errMsg *string
+	var data []byte
+
+	err := a.db.QueryRowContext(ctx, fmt.Sprintf(`
+		SELECT p_success, p_error, p_data::text
+		FROM %s($1)
+	`, a.sqlNames.OAuthExchangeCode), code).Scan(&success, &errMsg, &data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to exchange code: %w", err)
+	}
+	if !success {
+		if errMsg != nil {
+			return nil, fmt.Errorf("%s", *errMsg)
+		}
+		return nil, fmt.Errorf("invalid or expired code")
+	}
+
+	var result OAuthCode
+	if err := json.Unmarshal(data, &result); err != nil {
+		return nil, fmt.Errorf("failed to parse code data: %w", err)
+	}
+	result.Code = code
+	return &result, nil
+}
+
+// OAuthIntrospectToken validates a token and returns its metadata (RFC 7662).
+func (a *DatabaseAuthenticator) OAuthIntrospectToken(ctx context.Context, token string) (*OAuthTokenInfo, error) {
+	var success bool
+	var errMsg *string
+	var data []byte
+
+	err := a.db.QueryRowContext(ctx, fmt.Sprintf(`
+		SELECT p_success, p_error, p_data::text
+		FROM %s($1)
+	`, a.sqlNames.OAuthIntrospect), token).Scan(&success, &errMsg, &data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to introspect token: %w", err)
+	}
+	if !success {
+		if errMsg != nil {
+			return nil, fmt.Errorf("%s", *errMsg)
+		}
+		return nil, fmt.Errorf("introspection failed")
+	}
+
+	var result OAuthTokenInfo
+	if err := json.Unmarshal(data, &result); err != nil {
+		return nil, fmt.Errorf("failed to parse token info: %w", err)
+	}
+	return &result, nil
+}
+
+// OAuthRevokeToken revokes a token by deleting the session (RFC 7009).
+func (a *DatabaseAuthenticator) OAuthRevokeToken(ctx context.Context, token string) error {
+	var success bool
+	var errMsg *string
+
+	err := a.db.QueryRowContext(ctx, fmt.Sprintf(`
+		SELECT p_success, p_error
+		FROM %s($1)
+	`, a.sqlNames.OAuthRevoke), token).Scan(&success, &errMsg)
+	if err != nil {
+		return fmt.Errorf("failed to revoke token: %w", err)
+	}
+	if !success {
+		if errMsg != nil {
+			return fmt.Errorf("%s", *errMsg)
+		}
+		return fmt.Errorf("failed to revoke token")
+	}
+	return nil
+}

pkg/security/sql_names.go

@@ -54,6 +54,13 @@ type SQLNames struct {
 	OAuthUpdateRefreshToken string // default: "resolvespec_oauth_updaterefreshtoken"
 	OAuthGetUser            string // default: "resolvespec_oauth_getuser"
 
+	// OAuth2 server procedures (OAuthServer persistence)
+	OAuthRegisterClient string // default: "resolvespec_oauth_register_client"
+	OAuthGetClient      string // default: "resolvespec_oauth_get_client"
+	OAuthSaveCode       string // default: "resolvespec_oauth_save_code"
+	OAuthExchangeCode   string // default: "resolvespec_oauth_exchange_code"
+	OAuthIntrospect     string // default: "resolvespec_oauth_introspect"
+	OAuthRevoke         string // default: "resolvespec_oauth_revoke"
 }
 
 // DefaultSQLNames returns an SQLNames with all default resolvespec_* values.
@@ -93,6 +100,13 @@ func DefaultSQLNames() *SQLNames {
 		OAuthGetRefreshToken:    "resolvespec_oauth_getrefreshtoken",
 		OAuthUpdateRefreshToken: "resolvespec_oauth_updaterefreshtoken",
 		OAuthGetUser:            "resolvespec_oauth_getuser",
+
+		OAuthRegisterClient: "resolvespec_oauth_register_client",
+		OAuthGetClient:      "resolvespec_oauth_get_client",
+		OAuthSaveCode:       "resolvespec_oauth_save_code",
+		OAuthExchangeCode:   "resolvespec_oauth_exchange_code",
+		OAuthIntrospect:     "resolvespec_oauth_introspect",
+		OAuthRevoke:         "resolvespec_oauth_revoke",
 	}
 }
 
@@ -191,6 +205,24 @@ func MergeSQLNames(base, override *SQLNames) *SQLNames {
 	if override.OAuthGetUser != "" {
 		merged.OAuthGetUser = override.OAuthGetUser
 	}
+	if override.OAuthRegisterClient != "" {
+		merged.OAuthRegisterClient = override.OAuthRegisterClient
+	}
+	if override.OAuthGetClient != "" {
+		merged.OAuthGetClient = override.OAuthGetClient
+	}
+	if override.OAuthSaveCode != "" {
+		merged.OAuthSaveCode = override.OAuthSaveCode
+	}
+	if override.OAuthExchangeCode != "" {
+		merged.OAuthExchangeCode = override.OAuthExchangeCode
+	}
+	if override.OAuthIntrospect != "" {
+		merged.OAuthIntrospect = override.OAuthIntrospect
+	}
+	if override.OAuthRevoke != "" {
+		merged.OAuthRevoke = override.OAuthRevoke
+	}
 	return &merged
 }
 

pkg/server/example_test.go

@@ -3,6 +3,7 @@ package server_test
 import (
 	"context"
 	"fmt"
+	"log"
 	"net/http"
 	"time"
 
@@ -29,18 +30,18 @@ func ExampleManager_basic() {
 		GZIP:    true, // Enable GZIP compression
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Start all servers
 	if err := mgr.StartAll(); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Server is now running...
 	// When done, stop gracefully
 	if err := mgr.StopAll(); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 }
 
@@ -61,7 +62,7 @@ func ExampleManager_https() {
 		SSLKey:  "/path/to/key.pem",
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Option 2: Self-signed certificate (for development)
@@ -73,27 +74,27 @@ func ExampleManager_https() {
 		SelfSignedSSL: true,
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Option 3: Let's Encrypt / AutoTLS (for production)
 	_, err = mgr.Add(server.Config{
-		Name:           "https-server-letsencrypt",
+		Name:            "https-server-letsencrypt",
-		Host:           "0.0.0.0",
+		Host:            "0.0.0.0",
-		Port:           443,
+		Port:            443,
-		Handler:        handler,
+		Handler:         handler,
-		AutoTLS:        true,
+		AutoTLS:         true,
-		AutoTLSDomains: []string{"example.com", "www.example.com"},
+		AutoTLSDomains:  []string{"example.com", "www.example.com"},
-		AutoTLSEmail:   "admin@example.com",
+		AutoTLSEmail:    "admin@example.com",
 		AutoTLSCacheDir: "./certs-cache",
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Start all servers
 	if err := mgr.StartAll(); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Cleanup
@@ -136,7 +137,7 @@ func ExampleManager_gracefulShutdown() {
 		IdleTimeout:     120 * time.Second,
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Start servers and block until shutdown signal (SIGINT/SIGTERM)
@@ -164,7 +165,7 @@ func ExampleManager_healthChecks() {
 		Handler: mux,
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Add health and readiness endpoints
@@ -173,7 +174,7 @@ func ExampleManager_healthChecks() {
 
 	// Start the server
 	if err := mgr.StartAll(); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Health check returns:
@@ -204,7 +205,7 @@ func ExampleManager_multipleServers() {
 		GZIP:    true,
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Admin API server (different port)
@@ -218,7 +219,7 @@ func ExampleManager_multipleServers() {
 		Handler: adminHandler,
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Metrics server (internal only)
@@ -232,18 +233,18 @@ func ExampleManager_multipleServers() {
 		Handler: metricsHandler,
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Start all servers at once
 	if err := mgr.StartAll(); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Get specific server instance
 	publicInstance, err := mgr.Get("public-api")
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 	fmt.Printf("Public API running on: %s\n", publicInstance.Addr())
 
@@ -253,7 +254,7 @@ func ExampleManager_multipleServers() {
 
 	// Stop all servers gracefully (in parallel)
 	if err := mgr.StopAll(); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 }
 
@@ -273,11 +274,11 @@ func ExampleManager_monitoring() {
 		Handler: handler,
 	})
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	if err := mgr.StartAll(); err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 
 	// Check server status