Switch from Auth0 to self hosted KeyCloak

[joergreichert]

State of the art:

• Auth0 is used for user authentication
• one stop for authentication and issuing JWTs for frontend but also securing REST-APIs (trees API and user management API)
• free plan has ugly redirect to non LeipzigGiesst URL and restricted styling
• Basic plan cost 23$ a month but allows own auth URL and custom login screen design but changing something else in the application thus not used at the moment
• Multiple social logins offered, but currently feature switched off
• passwords of users are stored only at Auth0
• Auth0 is US-based so an issue GDPR-wise

motivation:

• be more GDPR-compatible
• more control

future state:

• we are hosting a properly configured https://www.keycloak.org on our server
• frontend and REST APIs are switched to KeyCloak
• existing users get notification to reregister again (as we have no access to their credentials at Auth0)

[joergreichert]

Superseeded by #22