* feat: support PKCE in authorization flow (RFC 7636)
* test: add tests for PKCE flow
* docs: document PKCE usage in OpenID client
* chore: address linting and formatting issues
* test: full e2e pkce test
* test: skip pkce for 22 and below
---------
Co-authored-by: Richard Nemeth <ryshoooo@gmail.com>