Add Auth0 authentication adapater

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

Parse Server currently does not support authentication using auth0.

Feature / Enhancement Description

Implement an authentication adapter for auth0; implementation could be very similar to the Google auth adapter since Auth0 also provides endpoints to the certs used for signing the tokens.

Example Use Case

Parse-based application that uses auth0 for authentication.

Alternatives / Workarounds

It would be possible to use the default oauth2 provider to implement authentication with auth0. However, this requires a query to the auth0 API for every login. Verifying the token directly in the Parse-Server using the certificates provided by Auth0, would improve latency and improve developer convenience.

3rd Party References

I would propose to follow the implementation of the current Google adapter closely.

If you approve of this proposal, I would implement the adapter and create PR, since I need it anyway for a project I am working on. I also saw that @davimacedo already proposed creating an adapter for Auth0 here.

Start by locating the existing Google authentication adapter and its certificate-verification entry points, then compare them with Auth0's certificate endpoints and token flow. Follow the adapter's existing tests if present; done means Auth0 users can authenticate through Parse Server without a per-login Auth0 API query.