AuthnBackend#Credentials: Clone breaks oauth2::PkceCodeVerifier

[Fyko]

oauth2::PkceCodeVerifier intentionally does not implement Clone to reinforce the integrity of the OAuth2 Process. This doesn't allow passing the value via fn authenticate(&self, credentials: Self::Credentials) as Credentials demands Clone.

[maxcountryman]

Maybe you can go into more detail about the specific flow you'd like to support.

In our OAuth2 example, we've set up Credentials like this:

axum-login/examples/oauth2/src/users.rs

Lines 45 to 48 in 8ed2bbc

	pub struct Credentials {
	pub code: String,
	pub old_state: CsrfToken,
	pub new_state: CsrfToken,

.

[maxcountryman]

I think this should also help: #157