Paid content block: swap login flow to magic link flow intead of code login flow

[simison]

Proposed changes:

• Adds magic link flow to paid content block, replacing the emailed code -flow

Methods copied from subscriber login block.

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

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

Testing instructions:

As already logged in subscriber, but not a paid customer, you won't see login button but will see subscribe button:

As logged out at site, but logged in at WP.com, login button simply logs you in:

Screen.Recording.2024-05-02.at.15.31.51.mov

As logged out at the site and logged out at WP.com, you'll go through the WP.com magic link flow and land back at the site:

[github-actions]

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 update/paid-content-auth-url branch.

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

  bin/jetpack-downloader test jetpack update/paid-content-auth-url
  

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]

Thank you for your PR!

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

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Jetpack plugin:

The Jetpack plugin has different release cadences depending on the platform:

• WordPress.com Simple releases happen daily.
• WoA releases happen weekly.
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[millerf]

LGTM

[simison]

Next up this would be good to move to a central place and share between the login block and this block:

jetpack/projects/plugins/jetpack/extensions/blocks/subscriber-login/subscriber-login.php

Lines 77 to 103 in 9bf534c

	/**
	* Returns subscriber log in URL.
	*
	* @param string $redirect Path to redirect to on login.
	*
	* @return string
	*/
	function get_subscriber_login_url( $redirect ) {
	$redirect = ! empty( $redirect ) ? $redirect : get_site_url();
	if ( ( new Host() )->is_wpcom_simple() ) {
	// On WPCOM we will redirect immediately
	return wpcom_logmein_redirect_url( $redirect, false, null, 'link', get_current_blog_id() );
	}
	// On self-hosted we will save and hide the token
	$redirect_url = get_site_url() . '/wp-json/jetpack/v4/subscribers/auth';
	$redirect_url = add_query_arg( 'redirect_url', $redirect, $redirect_url );
	return add_query_arg(
	array(
	'site_id' => intval( Jetpack_Options::get_option( 'id' ) ),
	'redirect_url' => rawurlencode( $redirect_url ),
	),
	'https://subscribe.wordpress.com/memberships/jwt/'
	);
	}