Register OAuth Rewrite Path

[akirk]

When a post exists on the WordPress site that includes the word "authorize", WordPress redirects there instead of letting EMA handle the path.

This adds the necessary rewrite routing for this. In the course I fixed two more bugs:

• We always flushed the rewrite on every request because we were not properly checking for the registered route (added the '^'
• We removed link headers from Gutenberg REST requests, this now limits that link removal to the prev and next as intended and also only for our own REST requests.

Fixes #129.

[akirk]

The tests fail because WordPress redirects to oauth/authorize/. The flow works (i.e. fixes the issue described in #129) for clients that support and follow those redirects but the test expects oauth/authorize to be served without a redirect. I think it's better for compatibility to avoid the redirect.

The responsible code is here in core: https://github.com/WordPress/wordpress-develop/blob/a4123728068e09200d7dfe2d5a88f803c1adf2aa/src/wp-includes/canonical.php#L695-L697

Which calls https://github.com/WordPress/wordpress-develop/blob/a4123728068e09200d7dfe2d5a88f803c1adf2aa/src/wp-includes/class-wp-query.php#L4345-L4348

And then https://github.com/WordPress/wordpress-develop/blob/a4123728068e09200d7dfe2d5a88f803c1adf2aa/src/wp-includes/class-wp-query.php#L1029-L1033

So rest routes get special treatment, I think this is what we need to convert this to.

[akirk]

I found another solution, so I think this is ready.