Body:

When configuring “Sign In with Apple” as an OAuth provider, Apple requires that if you request the name or email scopes, the authorize request must include response_mode=form_post. Otherwise, you receive the following error on login:

invalid_request
response_mode must be form_post when name or email scope is requested.

Currently, Fider’s provider configuration does not support adding custom/extra auth parameters, nor does it appear to automatically add this param for Apple. This means Sign In with Apple only works with the minimal openid scope (which provides no user info), and prevents receiving the user’s name/email as described in Apple’s docs.

Feature Request:
Please add support for setting custom authorization parameters—specifically, so Fider can send response_mode=form_post when name or email is requested from Apple.

References:

• Apple’s [Sign in with Apple docs](https://developer.apple.com/documentation/signinwithapplerestapi/request-an-authorization-to-the-sign-in-with-apple-server)
• Error example:
  ![screenshot or error text if you have it]

Impact:
Without this, “Sign in with Apple” in Fider can only provide pseudonymous Apple user IDs, and cannot collect user name/email for app onboarding or integration with existing registration flows.