feat: token endpoint

[balazsorban44]

EXPERIMENTAL

Reasoning 💡

A new take on #951

Checklist 🧢

• Documentation
• Tests
• Ready to be merged

Affected issues 🎟

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[balazsorban44]

OK, so the main issue here is if an access_token expires and let's say we start the token renewal by contacting the provider's /token endpoint, how do we make sure that subsequent requests under the renewal period does not cause a problem? It is especially hard, if the refresh_token is sliding (only usable once.).

My idea is that we need some kind of caching in the front-end that de-duplicates requests to this new /api/auth/token endpoint and rather subscribes to the result.

[balazsorban44]

Sorry for those who are eagerly waiting for this, and only see me keep closing it... My hunch about this PR fixing some problems wasn't right, so I have to close this again, as I prioritize other work for now. Could be an addition later in [email protected]. This is a new endpoint, so hopefully, it can be added in a non-breaking manner.