site-kit-wp: Incorrect redirects to WP Dashboard for sites with Internationalised Domain Names

Bug Description

On a site which uses IDNs (domains with multi-byte UTF-8 characters), redirects to the SiteKit dashboard are incorrectly directed to the WP Dashboard in various scenarios. This set of bugs were identified when implementing #4776.

Steps to reproduce

Scenario 1 - Setup SiteKit with Google Analytics

1. Go to ‘https://türkish.com/wp-admin’. Login using credentials which can be obtained from @wpdarren, @jamesozzie or @jimmymadon.
2. Setup SiteKit and tick the ‘Connect Google Analytics’ during SiteKit setup. After Step 4 - Connecting Google Analytics, instead of being redirected to the SiteKit dashboard, we are redirected to the WP Dashboard.
3. Navigate to the SiteKit dashboard. Google Analytics is still not connected.

Scenario 2 - Setup SiteKit without Google Analytics

1. Setup SiteKit but do not tick the ‘Connect Google Analytics’ during SiteKit setup. After Step 3, instead of being redirected to the SiteKit dashboard, we are redirected to the WP Dashboard.

Scenario 3 - Connect Analytics or AdSense

1. Go to Settings and attempt to connect AdSense.
2. After going through oAuth/setup, we are redirected back to WP Dashboard, and navigating back to settings shows that the set up is incomplete.

Additional Context

• PHP Version: 7.4.15
• OS: macOS 12.5.1
• Browser: Chrome Version 105.0.5195.102
• Plugin Version: 1.83.0
• Device: MacBook Pro 13
• WordPress Version: 6.0.2

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Acceptance criteria

• On sites which use multi-byte characters in their URLs / domain names (Internationalised Domain Names):
  • When setting up Site Kit, after the final step, the user should be redirected to the Site Kit dashboard as normal.
  • When setting up Site Kit with Analytics, the user should be redirected to the Site Kit dashboard as normal and Analytics should be connected successfully.
  • When connecting all modules in the plugin from the settings page, the module should be connected successfully and the user should be redirected to the Site Kit dashboard as normal.

Implementation Brief

• Replace the FILTER_SANITIZE_URL filter with FILTER_DEFAULT to avoid harming the redirect URL: https://github.com/google/site-kit-wp/blob/95dfa20a0ca7713a900c51f9ad100d0892f7cc79/includes/Core/Authentication/Setup.php#L131
• Replace wp_safe_redirect with just wp_redirect because the wp_safe_redirect breaks the internationalised domain in the wp_validate_redirect function: https://github.com/google/site-kit-wp/blob/95dfa20a0ca7713a900c51f9ad100d0892f7cc79/includes/Core/Authentication/Clients/OAuth_Client.php#L494

Test Coverage

• N/A

QA Brief

• Use a site with IDNs (eg. a domain with multi-byte UTF-8 characters, like türkish.com/xn--trkish-3ya.com)
• Set up a new install of Site Kit
• When setup is complete, you should be redirected back to the Site Kit dashboard (eg. /wp-admin/admin.php?page=googlesitekit-dashboard) and not the WordPress dashboard (eg. /wp-admin/admin.php)
• Do the same for AdSense and Analytics setup; you should also not be redirected to the main WordPress dashboard.

Changelog entry

• Fix incorrect redirects for sites with internationalized domain names.