It is not possible to login or register with internal auth

[LaChope]

When using internal auth (both development and production modes), I cannot login or register a new user. When I try to register a new user, I get denied. The API call is /auth/register.
@blcham @Kasmadei Can you check if this also happens to you?
@kostobog could it be because the backend needs a logged user even for public pages?

This issue is a blocker for #343.

Backend logs:

[blcham]

@LaChope It behaves the same for me, I investigated server log file, and this is the error:

[blcham]

@kostobog A similar issue happened so many times that we should at least talk about how to test JUnit tests (maybe would be hard to implement, but let's brainstorm about that)

[kostobog]

@blcham
This issue occurs due to a bad login and registration request.
The client sends jsonld with the wrong uri mapped to the username property in the context.

This inconsistency occurred when adjusting fta-fmea to be compatible with keyckloak docker distribution.