MDL-79725 libraries: fix auth URL generation in lti1p3 library

lib/lti1p3/readme_moodle.txt

@@ -5,6 +5,8 @@ This library is a patched for use in Moodle - it requires the following changes
 2. Removal of Guzzle dependency (replaced with generic http client interfaces which are more compatible with Moodle's curl.)
 3. Small fix to http_build_query() usages, to make sure the arg separator is explicitly set to '&', so as not to trip up
 on Moodle's definition of PHP's arg_separator.output which is set to '&' in lib/setup.php.
+4. Apply the fix from https://github.com/packbackbooks/lti-1-3-php-library/pull/107. If this is already merged upstream, please
+remove this line.
 
 To upgrade to a new version of this library:
 1. Clone the latest version of the upstream library from github:

lib/lti1p3/src/LtiOidcLogin.php

@@ -93,7 +93,12 @@ public function doOidcLoginRedirect($launch_url, array $request = null)
             $auth_params['lti_message_hint'] = $request['lti_message_hint'];
         }
 
-        $auth_login_return_url = $registration->getAuthLoginUrl().'?'.http_build_query($auth_params, '', '&');
+        if (parse_url($registration->getAuthLoginUrl(), PHP_URL_QUERY)) {
+            $separator = '&';
+        } else {
+            $separator = '?';
+        }
+        $auth_login_return_url = $registration->getAuthLoginUrl().$separator.http_build_query($auth_params, '', '&');
 
         // Return auth redirect.
         return new Redirect($auth_login_return_url, http_build_query($request, '', '&'));