AuthN: Fix signout redirect url (#87631)

* Add missing return

* Use sign out redirect url from auth config if configured

* remove option from auth.jwt that is not used

pkg/services/authn/authnimpl/service_test.go

@@ -409,7 +409,8 @@ func TestService_Logout(t *testing.T) {
 		identity     *authn.Identity
 		sessionToken *usertoken.UserToken
 
-		client authn.Client
+		client             authn.Client
+		signoutRedirectURL string
 
 		expectedErr          error
 		expectedTokenRevoked bool
@@ -441,6 +442,14 @@ func TestService_Logout(t *testing.T) {
 			client:               &authntest.FakeClient{ExpectedName: "auth.client.azuread"},
 			expectedTokenRevoked: true,
 		},
+		{
+			desc:                 "should use signout redirect url if configured",
+			identity:             &authn.Identity{ID: authn.NewNamespaceID(authn.NamespaceUser, 1), AuthenticatedBy: "azuread"},
+			expectedRedirect:     &authn.Redirect{URL: "some-url"},
+			client:               &authntest.FakeClient{ExpectedName: "auth.client.azuread"},
+			signoutRedirectURL:   "some-url",
+			expectedTokenRevoked: true,
+		},
 		{
 			desc:             "should redirect to client specific url",
 			identity:         &authn.Identity{ID: authn.NewNamespaceID(authn.NamespaceUser, 1), AuthenticatedBy: "azuread"},
@@ -473,6 +482,10 @@ func TestService_Logout(t *testing.T) {
 						return nil
 					},
 				}
+
+				if tt.signoutRedirectURL != "" {
+					svc.cfg.SignoutRedirectUrl = tt.signoutRedirectURL
+				}
 			})
 
 			redirect, err := s.Logout(context.Background(), tt.identity, tt.sessionToken)