Refactor scope validation

config.yaml

@@ -50,9 +50,9 @@ demo:
 resource_identifier: http://localhost:3000
 audience: mcp_proxy
 scopes_supported:
-  "read:tools"
+  - "tools":"read:tools"
-  "read:resources"
+  - "resources":"read:resources"
-  "read:prompts"
+  - "prompts":"read:prompts"
 authorization_servers:
   - https://api.asgardeo.io/t/acme/
 jwks_uri: https://api.asgardeo.io/t/acme/oauth2/jwks

internal/authz/default_policy_engine.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"net/http"
 	"strings"
+
+	logger "github.com/wso2/open-mcp-auth-proxy/internal/logging"
 )
 
 type TokenClaims struct {
@@ -16,30 +18,42 @@ type DefaultPolicyEngine struct{}
 func (d *DefaultPolicyEngine) Evaluate(
 	_ *http.Request,
 	claims *TokenClaims,
-	requiredScope string,
+	requiredScopes any,
 ) PolicyResult {
-	if strings.TrimSpace(requiredScope) == "" {
+
+	logger.Info("Required scopes: %v", requiredScopes)
+
+	var scopeStr string
+	switch v := requiredScopes.(type) {
+	case string:
+		scopeStr = v
+	case []string:
+		scopeStr = strings.Join(v, " ")
+	}
+
+	if strings.TrimSpace(scopeStr) == "" {
 		return PolicyResult{DecisionAllow, ""}
 	}
 
-	raw := strings.FieldsFunc(requiredScope, func(r rune) bool {
+	scopes := strings.FieldsFunc(scopeStr, func(r rune) bool {
 		return r == ' ' || r == ','
 	})
-	want := make(map[string]struct{}, len(raw))
+	required := make(map[string]struct{}, len(scopes))
-	for _, s := range raw {
+	for _, s := range scopes {
 		if s = strings.TrimSpace(s); s != "" {
-			want[s] = struct{}{}
+			required[s] = struct{}{}
 		}
 	}
 
-	for _, have := range claims.Scopes {
+	logger.Info("Token scopes: %v", claims.Scopes)
-		if _, ok := want[have]; ok {
+	for _, tokenScope := range claims.Scopes {
+		if _, ok := required[tokenScope]; ok {
 			return PolicyResult{DecisionAllow, ""}
 		}
 	}
 
 	var list []string
-	for s := range want {
+	for s := range required {
 		list = append(list, s)
 	}
 	return PolicyResult{

internal/authz/policy.go

@@ -15,5 +15,5 @@ type PolicyResult struct {
 }
 
 type PolicyEngine interface {
-    Evaluate(r *http.Request, claims *TokenClaims, requiredScope string) PolicyResult
+	Evaluate(r *http.Request, claims *TokenClaims, requiredScopes any) PolicyResult
 }

internal/config/config.go

@@ -105,7 +105,7 @@ type Config struct {
 	// Protected resource metadata
 	Audience               string   `yaml:"audience"`
 	ResourceIdentifier     string   `yaml:"resource_identifier"`
-	ScopesSupported        map[string]string `yaml:"scopes_supported"`
+	ScopesSupported        any      `yaml:"scopes_supported"`
 	AuthorizationServers   []string `yaml:"authorization_servers"`
 	JwksURI                string   `yaml:"jwks_uri,omitempty"`
 	BearerMethodsSupported []string `yaml:"bearer_methods_supported,omitempty"`

internal/proxy/proxy.go

@@ -175,20 +175,10 @@ func buildProxyHandler(cfg *config.Config, modifiers map[string]RequestModifier,
 				}
 				isSSE = true
 			} else {
-				claims, err := authorizeMCP(w, r, isLatestSpec, cfg)
+				if err := authorizeMCP(w, r, isLatestSpec, cfg, policyEngine); err != nil {
-				if err != nil {
 					http.Error(w, err.Error(), http.StatusForbidden)
 					return
 				}
-
-				if isLatestSpec {
-					scope := cfg.ScopesSupported[r.URL.Path]
-					pr := policyEngine.Evaluate(r, claims, scope)
-					if pr.Decision == authz.DecisionDeny {
-						http.Error(w, "Forbidden: "+pr.Message, http.StatusForbidden)
-						return
-					}
-				}
 			}
 
 			targetURL = mcpBase
@@ -310,15 +300,7 @@ func authorizeSSE(w http.ResponseWriter, r *http.Request, isLatestSpec bool, res
 }
 
 // Handles both v1 (just signature) and v2 (aud + scope) flows
-func authorizeMCP(w http.ResponseWriter, r *http.Request, isLatestSpec bool, cfg *config.Config) (*authz.TokenClaims, error) {
+func authorizeMCP(w http.ResponseWriter, r *http.Request, isLatestSpec bool, cfg *config.Config, policyEngine authz.PolicyEngine) error {
-	// Parse JSON-RPC request if present
-	if env, err := util.ParseRPCRequest(r); err != nil {
-		http.Error(w, "Bad request", http.StatusBadRequest)
-		return nil, err
-	} else if env != nil {
-		logger.Info("JSON-RPC method = %q", env.Method)
-	}
-
 	authzHeader := r.Header.Get("Authorization")
 	if !strings.HasPrefix(authzHeader, "Bearer ") {
 		if isLatestSpec {
@@ -329,35 +311,43 @@ func authorizeMCP(w http.ResponseWriter, r *http.Request, isLatestSpec bool, cfg
 			w.Header().Set("Access-Control-Expose-Headers", "WWW-Authenticate")
 		}
 		http.Error(w, "Unauthorized", http.StatusUnauthorized)
-        return nil, fmt.Errorf("missing or invalid Authorization header")
+		return fmt.Errorf("missing or invalid Authorization header")
 	}
 
-    requiredScope := ""
+	claims, err := util.ValidateJWT(isLatestSpec, authzHeader, cfg.Audience)
-    if isLatestSpec {
-        requiredScope = cfg.ScopesSupported[r.URL.Path]
-    }
-    claims, err := util.ValidateJWT(
-        isLatestSpec,
-        authzHeader,
-        cfg.Audience,
-        requiredScope,
-    )
 	if err != nil {
 		if isLatestSpec {
 			realm := cfg.ResourceIdentifier + "/.well-known/oauth-protected-resource"
-            w.Header().Set("WWW-Authenticate", fmt.Sprintf(
+			w.Header().Set("WWW-Authenticate", fmt.Sprintf(err.Error(),
-                `Bearer realm=%q, error="insufficient_scope", scope=%q`,
+				`Bearer realm=%q`,
-                realm, requiredScope,
+				realm,
 			))
 			w.Header().Set("Access-Control-Expose-Headers", "WWW-Authenticate")
 			http.Error(w, "Forbidden", http.StatusForbidden)
 		} else {
 			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 		}
-        return nil, err
+		return err
 	}
 
-    return claims, nil
+	if isLatestSpec {
+		env, err := util.ParseRPCRequest(r)
+		if err != nil {
+			http.Error(w, "Bad request", http.StatusBadRequest)
+			return err
+		}
+		requiredScopes := util.GetRequiredScopes(cfg, env.Method)
+		if len(requiredScopes) == 0 {
+			return nil
+		}
+		pr := policyEngine.Evaluate(r, claims, requiredScopes)
+		if pr.Decision == authz.DecisionDeny {
+			http.Error(w, "Forbidden: "+pr.Message, http.StatusForbidden)
+			return fmt.Errorf("forbidden — %s", pr.Message)
+		}
+	}
+
+	return nil
 }
 
 func getAllowedOrigin(origin string, cfg *config.Config) string {

internal/util/jwks.go

@@ -11,7 +11,8 @@ import (
 
 	"github.com/golang-jwt/jwt/v4"
 	"github.com/wso2/open-mcp-auth-proxy/internal/authz"
-	"github.com/wso2/open-mcp-auth-proxy/internal/logging"
+	"github.com/wso2/open-mcp-auth-proxy/internal/config"
+	logger "github.com/wso2/open-mcp-auth-proxy/internal/logging"
 )
 
 type TokenClaims struct {
@@ -80,19 +81,20 @@ func parseRSAPublicKey(nStr, eStr string) (*rsa.PublicKey, error) {
 }
 
 // ValidateJWT checks the Bearer token according to the Mcp-Protocol-Version.
-//   - versionHeader: the raw value of the "Mcp-Protocol-Version" header
+//   - isLatestSpec: whether to use the latest spec validation
 //   - authHeader:    the full "Authorization" header
 //   - audience:      the resource identifier to check "aud" against
-//   - requiredScope: the single scope required (empty ⇒ skip scope check)
+//   - requiredScopes: the scopes required (empty ⇒ skip scope check)
 func ValidateJWT(
-	isLatestSpec bool, authHeader, audience, requiredScope string,
+	isLatestSpec bool,
+	authHeader, audience string,
 ) (*authz.TokenClaims, error) {
 	tokenStr := strings.TrimPrefix(authHeader, "Bearer ")
 	if tokenStr == "" {
 		return nil, errors.New("empty bearer token")
 	}
 
-	// 2) parse & verify signature
+	// --- parse & verify signature ---
 	token, err := jwt.Parse(tokenStr, func(token *jwt.Token) (interface{}, error) {
 		if _, ok := token.Method.(*jwt.SigningMethodRSA); !ok {
 			return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
@@ -107,7 +109,6 @@ func ValidateJWT(
 		}
 		return key, nil
 	})
-
 	if err != nil {
 		return nil, fmt.Errorf("invalid token: %w", err)
 	}
@@ -115,18 +116,19 @@ func ValidateJWT(
 		return nil, errors.New("token not valid")
 	}
 
-	// always extract claims
+	// --- extract raw claims ---
 	claimsMap, ok := token.Claims.(jwt.MapClaims)
 	if !ok {
 		return nil, errors.New("unexpected claim type")
 	}
 
-	// if older than cutover, skip audience+scope
+	// --- v1: skip audience check entirely ---
 	if !isLatestSpec {
+		// we still want to return an empty set of scopes for policy to see
 		return &authz.TokenClaims{Scopes: nil}, nil
 	}
 
-	// --- new spec flow: enforce audience ---
+	// --- v2: enforce audience ---
 	audRaw, exists := claimsMap["aud"]
 	if !exists {
 		return nil, errors.New("aud claim missing")
@@ -151,25 +153,33 @@ func ValidateJWT(
 		return nil, errors.New("aud claim has unexpected type")
 	}
 
-	// if no scope required, we're done
+	// --- collect all scopes from the token, if any ---
-	if requiredScope == "" {
+	rawScope := claimsMap["scope"]
-		return &authz.TokenClaims{Scopes: nil}, nil
+	scopeList := []string{}
+	if s, ok := rawScope.(string); ok {
+		scopeList = strings.Fields(s)
 	}
 
-	// enforce scope
+	return &authz.TokenClaims{Scopes: scopeList}, nil
-	rawScope, exists := claimsMap["scope"]
+}
-	if !exists {
+
-		return nil, errors.New("scope claim missing")
+// Process the required scopes
-	}
+func GetRequiredScopes(cfg *config.Config, method string) []string {
-	scopeStr, ok := rawScope.(string)
+	if scopes, ok := cfg.ScopesSupported.(map[string]string); ok && len(scopes) > 0 {
-	if !ok {
+		if scope, ok := scopes[method]; ok {
-		return nil, errors.New("scope claim not a string")
+			return []string{scope}
-	}
+		}
-	scopes := strings.Fields(scopeStr)
+		if parts := strings.SplitN(method, "/", 2); len(parts) > 0 {
-	for _, s := range scopes {
+			if scope, ok := scopes[parts[0]]; ok {
-		if s == requiredScope {
+				return []string{scope}
-			return &authz.TokenClaims{Scopes: scopes}, nil
+			}
-		}
+		}
-	}
+		return nil
-	return nil, fmt.Errorf("insufficient scope: %q not in %v", requiredScope, scopes)
+	}
+
+	if scopes, ok := cfg.ScopesSupported.([]string); ok && len(scopes) > 0 {
+		return scopes
+	}
+
+	return []string{}
 }

internal/util/rpc.go

@@ -34,6 +34,5 @@ func ParseRPCRequest(r *http.Request) (*RPCEnvelope, error) {
 		return nil, err
 	}
 
-	logger.Info("JSON-RPC method = %q", env.Method)
 	return &env, nil
 }