* Add support for PKCE (Proof Key for Code Exchange, [RFC 7636](https://www.rfc-editor.org/rfc/rfc7636)) [#901](https://github.com/thephpleague/oauth2-client/pull/901) * Various type improvements for static analysis [#939](https://github.com/thephpleague/oauth2-client/pull/939) [#959](https://github.com/thephpleague/oauth2-client/pull/959) [#972](https://github.com/thephpleague/oauth2-client/pull/972) [#997](https://github.com/thephpleague/oauth2-client/pull/997)