feat(auth): implement OAuth 2.0 authorization code flow and dynamic client registration

- Add OAuth 2.0 support with authorization code flow and dynamic client registration.
- Introduce new handlers for OAuth metadata, client registration, authorization, and token issuance.
- Enhance authentication middleware to support OAuth client credentials.
- Create in-memory stores for authorization codes and tokens.
- Update configuration to include OAuth client details.
- Ensure validation checks for OAuth clients in the configuration.

internal/config/config.go

@@ -36,11 +36,11 @@ type MCPConfig struct {
 }
 
 type AuthConfig struct {
-	Mode            string   `yaml:"mode"`
-	HeaderName      string   `yaml:"header_name"`
-	QueryParam      string   `yaml:"query_param"`
-	AllowQueryParam bool     `yaml:"allow_query_param"`
-	Keys            []APIKey `yaml:"keys"`
+	HeaderName      string      `yaml:"header_name"`
+	QueryParam      string      `yaml:"query_param"`
+	AllowQueryParam bool        `yaml:"allow_query_param"`
+	Keys            []APIKey    `yaml:"keys"`
+	OAuth           OAuthConfig `yaml:"oauth"`
 }
 
 type APIKey struct {
@@ -49,6 +49,17 @@ type APIKey struct {
 	Description string `yaml:"description"`
 }
 
+type OAuthConfig struct {
+	Clients []OAuthClient `yaml:"clients"`
+}
+
+type OAuthClient struct {
+	ID           string `yaml:"id"`
+	ClientID     string `yaml:"client_id"`
+	ClientSecret string `yaml:"client_secret"`
+	Description  string `yaml:"description"`
+}
+
 type DatabaseConfig struct {
 	URL             string        `yaml:"url"`
 	MaxConns        int32         `yaml:"max_conns"`