Due to gerrit #14971, a 500 is raised :
2020/07/02 09:12:20 [error] 1493#0: *962 rewrite or internal redirection cycle while processing "/plugins/ldap/index.php", client: 172.22.0.6, server: tuleap-web.tuleap-aio-dev.docker, request: "GET /plugins/ldap/welcome HTTP/1.0", host: "tuleap-web.tuleap-aio-dev.docker", referrer: "https://tuleap-web.tuleap-aio-dev.docker/my/redirect.php?return_to=%2Fplugins%2Fldap%2Fwelcome"
It occurs when a ldap user is login for the first time after a mapping with an already existing Tuleap user.