Connection: allow using application password for site registration

[sergeymitr]

Proposed changes:

• Adjust REST API to allow site registration without WP nonce if an application password is used.

Other information:

• [ ] Have you written new tests for your changes, if applicable?
• [ ] Have you checked the E2E test CI results, and verified that your changes do not break them?
• [ ] Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

https://github.com/Automattic/vulcan/issues/555

Does this pull request change what data or activity we track or use?

No.

Testing instructions:

1. Disconnect Jetpack.
2. Run the cURL command to register the site with WPCOM:

   curl 'https://example.com/index.php?rest_route=/jetpack/v4/connection/register' -X POST -H 'Content-Type: application/json' --data-raw '{"from":"jetpack-app","plugin_slug":"jetpack"}'

   Confirm you get the invalid_user_permission_jetpack_connect error along with error message and 401 status code.

3. User "Jetpack Debug" plugin's "REST API Tester" to send a REST request:
   • route: jetpack/v4/connection/register
   • method: POST
   • body: {"from":"jetpack-app","plugin_slug":"jetpack"}
4. Confirm you receive the 403 "invalid_nonce" error.
5. Go to "Users -> Profile" and create an application password.
6. Run the same cURL command with additional -u username:app_password in the end.
7. Confirm it responded with an authorization URL, and the site is now connected in site-only mode.

[github-actions[bot]]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the add/jetpack-app-site-registration branch.
  • For jetpack-mu-wpcom changes, also add define( 'JETPACK_MU_WPCOM_LOAD_VIA_BETA_PLUGIN', true ); to your wp-config.php file.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack add/jetpack-app-site-registration

  bin/jetpack-downloader test jetpack-mu-wpcom-plugin add/jetpack-app-site-registration

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions[bot]]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• :white_check_mark: Include a description of your PR changes.
  
• :white_check_mark: Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
• :white_check_mark: Add testing instructions.
  
• :white_check_mark: Specify whether this PR includes any changes to data or privacy.
  
• :white_check_mark: Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation :robot:

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The e2e test report can be found here. Please note that it can take a few minutes after the e2e tests checks are complete for the report to be available.

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     • For most changes, including minor cross-team impacts.
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