Support getting 'code' param from POST request

I don't think this proposal matches with the protocol:

After the user returns to the client via the redirect URL, the application will get the authorization code from the URL and use it to request an access token.

Can you provide more background information?

Moving this to a support request and closing:

This can be implemented with minimal effort in your own code:

1. Extend \Drupal\oauth2_client\Controller\OauthResponse and override ::RedirectResponse() with your change.
2. Define a route for your controller
3. Override \Drupal\oauth2_client\Plugin\Oauth2Client\Oauth2ClientPluginBase::getRedirectUri in your client plugin to use your route instead of the module's controller route.

FatherShawn → closed merge request !16