Update grant_type parameter in configureOAuth2Auth to use query string format for consistency

Author: smoghe-bw

src/Controllers/BaseController.php

@@ -128,7 +128,7 @@ protected function configureOAuth2Auth(&$headers)
                     $this->config->getClientId() . ':' . $this->config->getClientSecret()
                 ),
             ],
-            Request\Body::form(['grant_type' => 'client_credentials'])
+            'grant_type=client_credentials'
         );
 
         if ($response->code < 200 || $response->code > 299 || !isset($response->body->access_token)) {