Extract a new REST controller from core `Authentication`

[aaemnnosttv]

Feature Description

Similar to the work we did in #5732, this issue is about extracting the REST related behavior into a new controller.

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Do not alter or remove anything below. The following sections will be managed by moderators only.

Acceptance criteria

• All rest routes registered and related helper methods and defined by the core Authentication class should be extracted to a new Google\Site_Kit\Core\Authentication\REST_Authentication_Controller class
  • An accompanying test case should be created for it, similar to others that exercises the REST endpoints it registers and all REST-related tests should move from AuthenticationTest to the controller's test case
  • Test coverage should be added for any untested endpoints
  • The controller should be registered within Authentication::register
• No change in behavior should be made/observable here

Implementation Brief

• [ ] Add Google\Site_Kit\Core\Authentication\REST_Authentication_Controller class
  • In construct method pass the Authentication instance, and set it as a class property so all the needed methods can be accessed easily.
  • Add register method, and move googlesitekit_apifetch_preload_paths and googlesitekit_rest_routes filters from Authentication class here
  • Move get_rest_routes method from Authentication class, and use it's instance from class property to access the needed methods there
• [ ] Update includes/Core/Authentication/Authentication.php
  • In construct, instantiate REST_Authentication_Controller class, passing $this, and invoke REST_Authentication_Controller::register method in the Authentication::register

Test Coverage

• Add REST_Authentication_ControllerTest.php
  • Add tests for googlesitekit_rest_routes and googlesitekit_apifetch_preload_paths
  • Move over the test_disconnect
  • Add test coverage for connection and authentication endpoints, confirming the data returned, and get-token, you can save it using OAuth_Client::OPTION_ACCESS_TOKEN

QA Brief

• Set up Site Kit on a new site
• Set up all modules and uninstall all modules

No errors should occur during authentication.

Changelog entry

• N/A

[eugene-manuilov]

IB ✔️

[mohitwp]

QA Update ✅

• Tested on dev envrironment.
• Done smoke testing.
• Verified all modules setup successfully.
• Verified all modules disconnected successfully.
• No console errors or dashboard errors found.

[aaemnnosttv]

@10upsimon I left a comment on the PR but there is a little bit of follow-up to do here. This is good to go for now, but let's open another issue to address the rest. Let me know if you have any questions, thanks!