requestUserInfo appends ?schema=openid to userinfo endpoint, which breaks LinkedIn OIDC login

[gkreitz]

The function requestUserInfo appends ?schema=openid to the userinfo endpoint URL. I'm unsure why, I've tried googling a bit and cannot find a reason but haven't found anything (for instance, https://openid.net/specs/openid-connect-core-1_0.html does not contain the word "schema"). The parameter goes back to the initial commit of this library, so commit history gives no clue.

Adding this parameter breaks logging in with LinkedIn ( https://learn.microsoft.com/en-us/linkedin/consumer/integrations/self-serve/sign-in-with-linkedin-v2 ), as their userinfo endpoint seems to check for extra query parameters and reject the request with a 403, and the message "Unpermitted fields present in PARAMETER: Data Processing Exception while processing fields [/schema]". The symptom when using the library is an OpenIDConnectClientException with the message "The communication to retrieve user data has failed with status code 403" (to help anyone debugging that error message find their way here).

Unless there's some reason to keep ?schema=openid, I'd propose simply removing it. That would also fix #388, and remove the need for #389. Alternatively, one could add some option/function to toggle the behavior.