We’ve implemented to the ‘Well Known’ spec for OIDC to be compliant with OpenID integrations like AWS Cognito. You can find the full details of that here:
https://api.twitch.tv/api/.well-known/openid-configuration
For reference, that results in a userinfo API of:
https://api.twitch.tv/api/oidc/userinfo
For a provider like AWS Cognito, all of this is behind the scenes work so it’s absent from the Developer Docs. However, it may be useful to add there.