I have Gerrit v3.0.0 running on my server, everything was working fine yesterday.
Here\'s my authentication method :
[auth]
type = http
For people who got stuck in this nightmare, there is a guide which describes how to deal with this kind of issues.
As the guide describes: you need to directly edit the External ID database and remove all the misbehaving External ID entries. Starting with Gerrit 2.15 the database got migrated to NoteDb so brace yourself.