Bug report

• I confirm this is a bug with Supabase, not with my own application.
• I confirm I have searched the Docs, GitHub Discussions, and Discord.

Describe the bug

I believe #2300 introduced a breaking change when it defaulted all OAuth Apps' clients to client_secret_basic and started enforcing the token_endpoint_auth_method. Existing clients which were using client_secret_post successfully are now returning the error:

invalid authentication method: client is registered for 'client_secret_basic' but 'client_secret_post' was used

This is proper functionality, but I wanted to raise this so the change can be documented and existing clients given a heads up.

To Reproduce

Only way to repro is to take a client created before #2300 was merged, which was successfully sending credentials in the POST body, and trying to use it now. The above error will be shown.