Hmm, that's odd we have no hook there (Note that we do have a hook for purging thumbnails - LocalFilePurgeThumbnails, but nothing for general article purging)

Would it make sense to hook [[mw:Manual:Hooks/TitleSquidURLs]] to get the list of URLs to purge?

It's certainly not how the hook is intended to be used (it's supposed to provide the list so extensions can add URLs) but the worst that can happen should be that extra URLs added by some other extension (depending on order called) miss getting purged. As the hook has only existed since MW 1.22, the number of affected extensions should be small.

Such a hook should definitely be added.

In T216225#5335375, @Krinkle wrote:

I believe you can use the EventRelayer interface for this. It does not yet have much documentation, but the following should get you in the right direction.

For a custom CDN purger:

• Enable $wgUseCDN so that CdnCacheUpdate runs. (Keep these off $wgCdnReboundPurgeDelay, $wgCdnServers, and $wgHTCPRouting).
• Configure the cdn-url-purges channel $wgEventRelayerConfig with an implementation that purges your CDN in the way that it requires.

See also:

• https://github.com/wikimedia/mediawiki/blob/1.32.3/includes/deferred/CdnCacheUpdate.php#L112-L127
• https://doc.wikimedia.org/mediawiki-core/master/php/classEventRelayer.html

The cdn-url-purges channel will be notified with a list of urls to purge in the CDN. As a site administrator, you'd configure $wgEventRelayerConfig['cdn-url-purges']. The extension could provide an EventRelayer subclass that handles messages for $channel === 'cdn-url-purges' in the way that your CDN provider requires. For example:

$wgUseCDN = true;
$wgEventRelayerConfig['cdn-url-purges'] = [
  'class' => MediaWiki\Extension\MyCloudFare\EventRelayer::class,
];