Move to thephpleague/oauth2-server 9.0

One test failure remaining

The merge request updates thephpleague/oauth2-server to 9.0.x

Breaking changes are listed at the release page https://github.com/thephpleague/oauth2-server/releases/tag/9.0.0, but most notably:

1. New: Strict typing and return types
2. Changed: some exceptions return a different status code and the error message data structure has changed
3. Refresh token scopes are now finalized again, so any invalid scopes are removed (this was the last test failure in #4)

Seems fine to include in the module's beta phase, but this is up to the module's maintainer

Looks good, thanks!

Automatically closed - issue fixed for 2 weeks with no activity.