Finally the RFC Best Current Practice for OAuth 2.0 Security has been approved.
According to the RFC:
> Authorization servers MUST support PKCE [RFC7636].
>
> If a client sends a valid PKCE code_challenge parameter in the authorization request, the authorization server MUST enforce the correct usage of code_verifier at the token endpoint.
Isn’t it time we strengthen PKCE support a bit more?
This PR updates the logic so that PKCE is always verified, even when the Auth Method is not "none".
