diff --git a/pkg/oidc/token_request.go b/pkg/oidc/token_request.go
index 800c515..e80d28a 100644
--- a/pkg/oidc/token_request.go
+++ b/pkg/oidc/token_request.go
@@ -43,7 +43,7 @@ type JWTTokenRequest struct {
 	ExpiresAt Time     `json:"exp"`
 }
 
-//GetSubject implements the Claims interface
+//GetIssuer implements the Claims interface
 func (j *JWTTokenRequest) GetIssuer() string {
 	return j.Issuer
 }
diff --git a/pkg/op/storage.go b/pkg/op/storage.go
index e220c15..eba5003 100644
--- a/pkg/op/storage.go
+++ b/pkg/op/storage.go
@@ -26,11 +26,11 @@ type AuthStorage interface {
 }
 
 type OPStorage interface {
-	GetClientByClientID(context.Context, string) (Client, error)
-	AuthorizeClientIDSecret(context.Context, string, string) error
-	GetUserinfoFromScopes(context.Context, string, string, []string) (oidc.UserInfo, error)
+	GetClientByClientID(ctx context.Context, clientID string) (Client, error)
+	AuthorizeClientIDSecret(ctx context.Context, clientID, clientSecret string) error
+	GetUserinfoFromScopes(ctx context.Context, userID, clientID string, scopes []string) (oidc.UserInfo, error)
 	GetUserinfoFromToken(ctx context.Context, tokenID, subject, origin string) (oidc.UserInfo, error)
-	GetPrivateClaimsFromScopes(context.Context, string, string, []string) (map[string]interface{}, error)
+	GetPrivateClaimsFromScopes(ctx context.Context, userID, clientID string, scopes []string) (map[string]interface{}, error)
 	GetKeyByIDAndUserID(ctx context.Context, keyID, userID string) (*jose.JSONWebKey, error)
 }
 
diff --git a/pkg/utils/marshal_test.go b/pkg/utils/marshal_test.go
new file mode 100644
index 0000000..f9221f6
--- /dev/null
+++ b/pkg/utils/marshal_test.go
@@ -0,0 +1,60 @@
+package utils
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestConcatenateJSON(t *testing.T) {
+	type args struct {
+		first  []byte
+		second []byte
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    []byte
+		wantErr bool
+	}{
+		{
+			"invalid first part, error",
+			args{
+				[]byte(`invalid`),
+				[]byte(`{"some": "thing"}`),
+			},
+			nil,
+			true,
+		},
+		{
+			"invalid second part, error",
+			args{
+				[]byte(`{"some": "thing"}`),
+				[]byte(`invalid`),
+			},
+			nil,
+			true,
+		},
+		{
+			"both valid, merged",
+			args{
+				[]byte(`{"some": "thing"}`),
+				[]byte(`{"another": "thing"}`),
+			},
+
+			[]byte(`{"some": "thing","another": "thing"}`),
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ConcatenateJSON(tt.args.first, tt.args.second)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ConcatenateJSON() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !bytes.Equal(got, tt.want) {
+				t.Errorf("ConcatenateJSON() got = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}