make sure the user_oidc login does not redirect to logout (when allow_multiple_user_backends == 0)

Signed-off-by: Julien Veyssier <julien-nc@posteo.net>

Author: julien-nc

lib/AppInfo/Application.php

@@ -97,6 +97,12 @@ private function registerRedirect(IRequest $request, IURLGenerator $urlGenerator
 			// in case any errors happen when checking for the path do not apply redirect logic as it is only needed for the login
 		}
 		if ($isDefaultLogin && !$settings->getAllowMultipleUserBackEnds() && count($providers) === 1) {
+			// To avoid login/logout loop if the IdP session is still alive:
+			// if the login page's redirect_url GET param is the logout page, just use the base URL instead
+			$logoutUrl = $urlGenerator->linkToRoute('core.login.logout');
+			if (strpos($redirectUrl, $logoutUrl) !== false) {
+				$redirectUrl = $urlGenerator->getBaseUrl();
+			}
 			$targetUrl = $urlGenerator->linkToRoute(self::APP_ID . '.login.login', [
 				'providerId' => $providers[0]->getId(),
 				'redirectUrl' => $redirectUrl