diff --git a/oauth/get_token_context.go b/oauth/get_token_context.go
index 5ed23a30..6caea2fd 100644
--- a/oauth/get_token_context.go
+++ b/oauth/get_token_context.go
@@ -21,6 +21,14 @@ type cachedToken struct {
 var tokenMap sync.Map
 var clientMap sync.Map
 
+type tokenCacheKey struct {
+	NFType   models.NrfNfManagementNfType
+	TargetNF models.NrfNfManagementNfType
+	NFID     string
+	NRFURI   string
+	Scope    string
+}
+
 func GetTokenCtx(
 	nfType, targetNF models.NrfNfManagementNfType,
 	nfId, nrfUri, scope string,
@@ -49,7 +57,10 @@ func sendAccTokenReq(
 	}
 
 	// Check if we have a valid cached token
-	if val, ok := tokenMap.Load(scope); ok {
+	cacheKey := tokenCacheKey{
+		NFType: nfType, TargetNF: targetNF, NFID: nfId, NRFURI: nrfUri, Scope: scope,
+	}
+	if val, ok := tokenMap.Load(cacheKey); ok {
 		cached := val.(cachedToken)
 		// Compare current time with absolute expiry timestamp
 		if time.Now().Unix() < cached.ExpiryTime {
@@ -79,7 +90,7 @@ func sendAccTokenReq(
 			Response:   res.NrfAccessTokenAccessTokenRsp,
 			ExpiryTime: expiryTime,
 		}
-		tokenMap.Store(scope, cached)
+		tokenMap.Store(cacheKey, cached)
 
 		token := &oauth2.Token{
 			AccessToken: res.NrfAccessTokenAccessTokenRsp.AccessToken,
@@ -91,3 +102,4 @@ func sendAccTokenReq(
 		return nil, nil, openapi.ReportError("server no response")
 	}
 }
+
diff --git a/oauth/oauth.go b/oauth/oauth.go
index 9a9827fb..708bf711 100644
--- a/oauth/oauth.go
+++ b/oauth/oauth.go
@@ -16,8 +16,6 @@ import (
 
 	"github.com/golang-jwt/jwt/v5"
 	"github.com/pkg/errors"
-
-	"github.com/free5gc/openapi/models"
 )
 
 type CCAClaims struct {
@@ -26,6 +24,15 @@ type CCAClaims struct {
 	jwt.RegisteredClaims
 }
 
+// accessTokenClaims deliberately uses only jwt.RegisteredClaims for the
+// standard JWT fields. The generated free5GC model exposes duplicate iss,
+// sub, aud, and exp fields alongside RegisteredClaims; decoding into that
+// model leaves the validator's embedded fields empty.
+type accessTokenClaims struct {
+	Scope string `json:"scope,omitempty"`
+	jwt.RegisteredClaims
+}
+
 func GenerateClientCredentialAssertion(
 	sub, aud, keyPath string,
 ) (string, error) {
@@ -63,14 +70,14 @@ func VerifyOAuth(
 	}
 
 	auth_fields := strings.Fields(authorization)
-	if len(auth_fields) < 2 {
+	if len(auth_fields) != 2 || !strings.EqualFold(auth_fields[0], "Bearer") {
 		return errors.Errorf("verify OAuth Authorization header invalid")
 	}
 
 	access_token := auth_fields[1]
 	token, err := jwt.ParseWithClaims(
 		access_token,
-		&models.NrfAccessTokenAccessTokenClaims{},
+		&accessTokenClaims{},
 		func(token *jwt.Token) (interface{}, error) {
 			if _, ok := token.Method.(*jwt.SigningMethodRSA); !ok {
 				return nil, errors.Wrapf(err, "Unexpected signing method")
@@ -84,7 +91,7 @@ func VerifyOAuth(
 		return errors.Wrapf(err, "verify OAuth parse")
 	}
 
-	if !verifyScope(token.Claims.(*models.NrfAccessTokenAccessTokenClaims).Scope, serviceName) {
+	if !verifyScope(token.Claims.(*accessTokenClaims).Scope, serviceName) {
 		return errors.New("OAuth scope verification failed: insufficient permissions")
 	}
 	return nil
@@ -304,3 +311,4 @@ func GetNFCertPath(base, nfType, nfId string) string {
 	// Note: NF's cert should be put in the same base path
 	return filepath.Join(base, GetNFCertFileName(nfType, nfId))
 }
+
diff --git a/oauth/oauth_hardening_test.go b/oauth/oauth_hardening_test.go
new file mode 100644
index 00000000..e8c2d592
--- /dev/null
+++ b/oauth/oauth_hardening_test.go
@@ -0,0 +1,55 @@
+package oauth
+
+import (
+	"testing"
+	"time"
+
+	"github.com/free5gc/openapi/models"
+	"github.com/golang-jwt/jwt/v5"
+)
+
+func TestVerifyOAuthRejectsExpiredGeneratedModelToken(t *testing.T) {
+	dir := t.TempDir()
+	pubPath, privPath := dir+"/public.pem", dir+"/private.pem"
+	key, err := GenerateRSAKeyPair(pubPath, privPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	claims := models.AccessTokenClaims{
+		Scope: "svc",
+		Exp:   int32(time.Now().Add(-time.Minute).Unix()),
+		RegisteredClaims: jwt.RegisteredClaims{
+			Issuer: "issuer",
+		},
+	}
+	tok := jwt.NewWithClaims(jwt.SigningMethodRS512, claims)
+	signed, err := tok.SignedString(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := VerifyOAuth("Bearer "+signed, "svc", pubPath); err == nil {
+		t.Fatal("expired token was accepted")
+	}
+}
+
+func TestVerifyOAuthRequiresBearerScheme(t *testing.T) {
+	dir := t.TempDir()
+	pubPath, privPath := dir+"/public.pem", dir+"/private.pem"
+	key, err := GenerateRSAKeyPair(pubPath, privPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	claims := models.AccessTokenClaims{
+		Scope: "svc",
+		Exp:   int32(time.Now().Add(time.Minute).Unix()),
+	}
+	tok := jwt.NewWithClaims(jwt.SigningMethodRS512, claims)
+	signed, err := tok.SignedString(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := VerifyOAuth("Basic "+signed, "svc", pubPath); err == nil {
+		t.Fatal("non-Bearer authorization scheme was accepted")
+	}
+}
+