The redirect URI in the request, http://der-ls-treffpunkt.de/google-auth/, does not match the ones authorized for the OAuth client. To update the authorized redirect URIs, visit: https://console.developers.google.com/apis/credentials/oauthclient/283769543496-92tgp01nb81m1ilnjvcd2ai0uksuj4dc.apps.googleusercontent.com?project=283769543496