589 token url

[ewan-escience]

Remove token endpoints from config

Changes proposed in this pull request:

• Remove the *_TOKEN_URL env variables and adapt the auth module so that the token URL is queried from the well known URL on every request
• Give the reason when you login with e.g. GitHub through Helmholtz AAI and HELMHOLTZAAI_ALLOW_EXTERNAL_USERS=false

How to test:

• Remove *_TOKEN_URL values from your .env (see env.example)
• docker-compose build auth && docker-compose up
• Set HELMHOLTZAAI_ALLOW_EXTERNAL_USERS=true
• Login with all three providers, this should work
• Set HELMHOLTZAAI_ALLOW_EXTERNAL_USERS=false
• Login with Helmholtz AAI through GitHub or ORCID, you should see in red text You are not allowed to login

Discussion point

Maybe we should cache the token URL instead of querying it on every login. On my tests, ORCID was slow, taking 200 -- 900 ms. Helmholtz and SURF were below 100 ms.

Closes #589

PR Checklist:

• Increase version numbers in docker-compose.yml
• Link to a GitHub issue
• Update documentation
• Tests

[dmijatovic]

Nice work!

[cmeessen]

Works like a charm, the new error messages are really helpful 👍