are such variants bad:
https://github.com/scribejava/scribejava/pull/821/files
#739
As far as I remember, they was ok with enum

This implementation overrides the createAccessTokenRequest method of OAuth20Service and accomplishes similar functions 。

This is not necessary. All we have to do is add a custom client authentication method. This violates the original intention of the ClientAuthenticationType design.

Of course, no matter how wechat is implemented, our focus is on https://tools.ietf.org/html/rfc6749#section-2.3.2

We should provide a possible way for users to implement

It does make sense. Thank for pointing to this. I need some time to think about this.

This is only a minor change and will not affect other existing classes.
you can accept the pull request without additional burden