MDL-63994 auth_cas: Include the login token in the simulated login form

The CAS login process relies on the standard authenticate_user_login()
call to set up the user. So we need to inject the login token to pass
the validation.

auth/cas/auth.php

@@ -154,6 +154,7 @@ class auth_plugin_cas extends auth_plugin_ldap {
             $frm = new stdClass();
             $frm->username = phpCAS::getUser();
             $frm->password = 'passwdCas';
+            $frm->logintoken = \core\session\manager::get_login_token();
 
             // Redirect to a course if multi-auth is activated, authCAS is set to CAS and the courseid is specified.
             if ($this->config->multiauth && !empty($courseid)) {
@@ -167,6 +168,7 @@ class auth_plugin_cas extends auth_plugin_ldap {
             $frm = new stdClass();
             $frm->username = 'guest';
             $frm->password = 'guest';
+            $frm->logintoken = \core\session\manager::get_login_token();
             return;
         }