Make getClient() hookable to change the client's authentication method.

[elabx]

There is a way with Google's API to use the API's services without the Ouath2 authentication, using something called service accounts.

I've built a module that overrides the getClient() method so that it's easier to just swap the client with one that is trying to authenticate using a service account json secret auth like this:

class ServiceAccountForGoogleClient extends WireData implements Module {

	public static function getModuleInfo() {
		return array(
			'title' => 'GoogleClientAPI Service Account Hook',
			'summary' => 'Provides service-account authentication for GoogleClientAPI without modifying the original module.',
			'author' => 'Eduardo San Miguel',
			'icon' => 'key',
			'version' => 1,
			'autoload' => true,
			'singular' => true,
			'requires' => array('ProcessWire>=3.0.0', 'GoogleClientAPI'),
		);
	}

	public function init() {
		// Hook before getClient so we can replace it entirely for service accounts
		if(!(int) $this->enabled) return;

		$this->addHookBefore('GoogleClientAPI::getClient', function(HookEvent $event) {
			
			$authConfig = $this->serviceAccountJson;
			if(!$authConfig) throw new WireException('Service account authentication is not configured');


			$authConfig = json_decode($authConfig, true);

			if((string) ($authConfig['type'] ?? '') !== 'service_account') throw new WireException('Service account authentication is not configured'); // not a service account, let original getClient() run

			// Merge options similar to GoogleClientAPI::getClient			
			$client = new \Google_Client();
			
			$client->setAuthConfig($authConfig);
			$client->setScopes($this->scopes);

			$event->return = $client; // return our client
			$event->replace = true;   // prevent original getClient() from running
		});
	}
}

Altough this solution depends on getClient() being hookable.