Enable login with DataPLANT account

[Freymaurer]

This can be done actively, instead of the captcha or even passively.

Actively: log in with username/email and password, this is sent to the heldesk backend, which forwards it towards keycloak to do the whole oauth authorisation cycle, send token to client for session storage. Verify token on issue submit.

Passively: No active username, pw input. User must be logged in already. Get token from cookies/local storage/proxy. Verify token on issue submit.