ejabberd

https://docs.ejabberd.im/admin/configuration/

Web admin

https://docs.ejabberd.im/admin/guide/managing/#web-admin

You need to use full “user@domain.org” to authenticate. Make sure that admin acl is set for “user” not for “user@domain”, to work for all virtualhosts.

Find passwords

ejabberctl dump config

Look for file config and find lines:

{passwd,{<<"user1">>,<<"hostname.com">>},<<"secret1">>}.
{passwd,{<<"user2">>,<<"hostname.com">>},<<"secret1">>}.