PKCE support for OAuth2 #182
Description
Feature request
My understanding is OAuth 2.1 will require PKCE, and this is the default mechanism for Keycloak and Zitadel.
https://datatracker.ietf.org/doc/html/rfc7636#section-4.1 contains the detailed spec, but the gist is to generate a random code_verifier value and a hashed code_challenge in lieu of storing a client secret in the app.
My expedient solution is to modify runOAuth2, authorizationUrl and tokenParams in a local fork and add crypton as a dependency but that's probably invasive for any existing users of the library.