Feature: JWT decoding

[ocramz]

Many OAuth2 access tokens seem to be JWT-encoded and I often decode them to obtain an user ID (e.g. from the 'sub' field of JWT). This is not strictly standard but the industry seems to be moving in this direction https://datatracker.ietf.org/doc/html/draft-ietf-oauth-access-token-jwt-10

Using something like jwt package perhaps we could add a helper function OAuth2 -> Validation [Text] JWT or similar

[ocramz]

I've made a PR to jwt https://github.com/puffnfresh/haskell-jwt/pull/7 that if accepted could come in handy here as well.

[freizl]

Good point! I'll be thinking to create another package like hoauth2-jwt which has helpers for access token and ID token validation if it's JWT.