Implement Token introspection endpoint onto Dex

[supercairos]

Preflight Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

I'm trying to integrate Dex with Ory/Oathkeeper that use the introspect endpoint in order to validate the token.
And I'm realizing that Dex doesn't support the token introspection endpoint.

Proposed Solution

Implement the Token introspection endpoint onto Dex:
https://www.oauth.com/oauth2-servers/token-introspection-endpoint
https://datatracker.ietf.org/doc/html/rfc7662

Alternatives Considered

No response

Additional Information

No response

[chilledtonic]

Seconding this as a feature. This would be incredibly useful to use Dex as a bridge between older Oauth implementations that may not see new RFCs being added.

[nabokihms]

Great idea for a contribution! I'd really like to take this in.

[supercairos]

I can work on that :)

Hopefully It will be an easy first issue 🙏