WAF: Fix request body problem

[dkmyta]

Fixes #
The WAF currently defaults to retrieving values from $_POST when the provided Content-Type isn't "application/json". This works and is a very simple way to not parse everything ourselves. However, it also means that it won't retrieve any parameters whatsoever if the HTTP method used isn't POST, since PHP will not populate $_POST in those cases.

Proposed changes:

• Similar to the handling in the WordPress API, we will now parse the request body when the method used is not POST.

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/jetpack-scan-team/issues/1177

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

• No

Testing instructions:

• Ensure that the new logic covers cases like curl --url $URL -X PATCH --data 'test=<script>alert(1);</script>'
• Run unit tests and verify they all succeed
• Verify no regressions are introduced

[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 fix/waf-request-body-problem branch.

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  bin/jetpack-downloader test jetpack fix/waf-request-body-problem
  

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[github-actions]

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[nateweller]

Change looks good! Introduces the functionality nicely.

I've tested triggering the XSS rule with a foo=<script> payload using POST, PUT, and PATCH requests with success across Form-URL-Encoded, JSON, and Text Content-Types. 👍

[nateweller]

LGTM!