MDL-87119 login: Improve the logout confirmation dialogue

public/lang/en/moodle.php

@@ -1247,6 +1247,7 @@ $string['loginrequired'] = 'Login required';
 $string['logoof'] = 'Logo of {$a}';
 $string['logout'] = 'Log out';
 $string['logoutconfirm'] = 'Do you really want to log out?';
+$string['logoutconfirmtitle'] = 'Log out?';
 $string['logs'] = 'Logs';
 $string['logtoomanycourses'] = '[ <a href="{$a->url}">more</a> ]';
 $string['logtoomanyusers'] = '[ <a href="{$a->url}">more</a> ]';

public/login/index.php

@@ -394,8 +394,13 @@ if (isloggedin() and !isguestuser()) {
     // prevent logging when already logged in, we do not want them to relogin by accident because sesskey would be changed
     echo $OUTPUT->box_start();
     $logout = new single_button(new moodle_url('/login/logout.php', array('sesskey'=>sesskey(),'loginpage'=>1)), get_string('logout'), 'post');
-    $continue = new single_button(new moodle_url('/'), get_string('cancel'), 'get');
-    echo $OUTPUT->confirm(get_string('alreadyloggedin', 'error', fullname($USER)), $logout, $continue);
+    $continue = new single_button(new moodle_url('/'), get_string('gobacktosite'), 'get');
+    echo $OUTPUT->confirm(
+        message: get_string('alreadyloggedin', 'error', fullname($USER)),
+        continue: $logout,
+        cancel: $continue,
+        displayoptions: ['confirmtitle' => get_string('logoutconfirmtitle')],
+    );
     echo $OUTPUT->box_end();
 } else {
     $loginform = new \core_auth\output\login($authsequence, $frm->username);

public/login/tests/behat/relogin.feature

@@ -0,0 +1,21 @@
+@core
+Feature: Relogin prevention
+  User will be informed when trying to login again while already logged in
+  As a user
+  I should be informed that I am already logged in
+
+  Background:
+    Given the following "users" exist:
+      | username | password | firstname | lastname | email            |
+      | testuser | test     | Test      | User     | user@example.com |
+
+  Scenario: A logged in user tries to access the login page again
+    Given I follow "Log in"
+    And I set the field "Username" to "testuser"
+    And I set the field "Password" to "test"
+    And I press "Log in"
+    And I should see "You are logged in as"
+    When I visit "/login"
+    Then I should see "You are already logged in as Test User, you need to log out before logging in as different user." in the "Log out?" "dialogue"
+    And "Go back to site" "button" should exist in the "Log out?" "dialogue"
+    And "Log out" "button" should exist in the "Log out?" "dialogue"