MDL-80835 enrol_lti: add cookies required notice to auth login endpoint

This will be displayed if the cookie checks fail, which currently occurs
in Safari only.

enrol/lti/classes/output/renderer.php

@@ -263,4 +263,19 @@ class renderer extends plugin_renderer_base {
         return parent::render_from_template('enrol_lti/local/ltiadvantage/registration_view',
             $tcontext);
     }
+
+    /**
+     * Render a warning, indicating to the user that cookies are require but couldn't be set.
+     *
+     * @return string the html.
+     */
+    public function render_cookies_required_notice(): string {
+        $notification = new notification(get_string('cookiesarerequiredinfo', 'enrol_lti'), notification::NOTIFY_WARNING, false);
+        $tcontext = [
+            'heading' => get_string('cookiesarerequired', 'enrol_lti'),
+            'notification' => $notification->export_for_template($this),
+        ];
+
+        return parent::render_from_template('enrol_lti/local/ltiadvantage/cookies_required_notice', $tcontext);
+    }
 }

enrol/lti/lang/en/enrol_lti.php

@@ -31,6 +31,10 @@ $string['addtocourse'] = 'Add to course';
 $string['addtogradebook'] = 'Add to gradebook';
 $string['allowframeembedding'] = 'Note: It is recommended that the site administration setting \'Allow frame embedding\' is enabled, so that tools are displayed within a frame rather than in a new window.';
 $string['authltimustbeenabled'] = 'Note: This plugin requires the LTI authentication plugin to be enabled too.';
+$string['cookiesarerequired'] = 'Cookies are blocked by your browser';
+$string['cookiesarerequiredinfo'] = 'This tool can\'t be launched because your browser seems to be blocking third-party cookies.
+<br><br>
+To use this tool, try changing your browser cookie settings or using a different browser.';
 $string['copiedtoclipboard'] = '{$a} copied to clipboard';
 $string['copytoclipboard'] = 'Copy to clipboard';
 $string['couldnotestablishproxy'] = 'Could not establish proxy with consumer.';

enrol/lti/login.php

@@ -88,6 +88,17 @@ if (!isloggedin()) {
         'lti_message_hint' => $ltimessagehint,
         'client_id' => $_REQUEST['client_id'],
     ]));
+    if (!cookie_helper::cookies_supported()) {
+        global $OUTPUT, $PAGE;
+        $PAGE->set_context(context_system::instance());
+        $PAGE->set_url(new moodle_url('/enrol/lti/login.php'));
+        $PAGE->set_pagelayout('popup');
+        echo $OUTPUT->header();
+        $renderer = $PAGE->get_renderer('enrol_lti');
+        echo $renderer->render_cookies_required_notice();
+        echo $OUTPUT->footer();
+        die();
+    }
 }
 
 // Now, do the OIDC login.

enrol/lti/templates/local/ltiadvantage/cookies_required_notice.mustache

@@ -0,0 +1,50 @@
+{{!
+    This file is part of Moodle - http://moodle.org/
+
+    Moodle is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Moodle is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+}}
+{{!
+    @template enrol_lti/local/ltiadvantage/cookies_required_notice
+
+    Displays a notice, reporting that cookies are required but couldn't be set.
+
+    Classes required for JS:
+    * none
+
+    Data attributes required for JS:
+    * none
+
+    Context variables required for this template:
+    * heading
+    * notification
+
+    Example context (json):
+    {
+        "heading": "Cookies are required",
+        "notification": {
+            "message": "You appear to be using an unsupported browser...",
+            "extraclasses": "",
+            "announce": true,
+            "closebutton": false,
+            "issuccess": false,
+            "isinfo": false,
+            "iswarning": true,
+            "iserror": false
+        }
+    }
+}}
+<h3>{{heading}}</h3>
+{{#notification}}
+    {{> core/notification}}
+{{/notification}}