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/auth/oauth_registry.go

@@ -0,0 +1,33 @@
+package auth
+
+import (
+	"crypto/subtle"
+	"fmt"
+
+	"git.warky.dev/wdevs/amcs/internal/config"
+)
+
+type OAuthRegistry struct {
+	clients []config.OAuthClient
+}
+
+func NewOAuthRegistry(clients []config.OAuthClient) (*OAuthRegistry, error) {
+	if len(clients) == 0 {
+		return nil, fmt.Errorf("oauth registry requires at least one client")
+	}
+
+	return &OAuthRegistry{clients: append([]config.OAuthClient(nil), clients...)}, nil
+}
+
+func (o *OAuthRegistry) Lookup(clientID string, clientSecret string) (string, bool) {
+	for _, client := range o.clients {
+		if subtle.ConstantTimeCompare([]byte(client.ClientID), []byte(clientID)) == 1 &&
+			subtle.ConstantTimeCompare([]byte(client.ClientSecret), []byte(clientSecret)) == 1 {
+			if client.ID != "" {
+				return client.ID, true
+			}
+			return client.ClientID, true
+		}
+	}
+	return "", false
+}