diff --git a/lib/authlib.php b/lib/authlib.php
index dc2ceb90f0c..cb9ef99ecbc 100644
--- a/lib/authlib.php
+++ b/lib/authlib.php
@@ -435,6 +435,26 @@ class auth_plugin_base {
         //override if needed
     }
 
+    /**
+     * Hook for overriding behaviour before going to the login page.
+     *
+     * This method is called from require_login from potentially any page for
+     * all enabled auth plugins and gives each plugin a chance to redirect
+     * directly to an external login page, or to instantly login a user where
+     * possible.
+     *
+     * If an auth plugin implements this hook, it must not rely on ONLY this
+     * hook in order to work, as there are many ways a user can browse directly
+     * to the standard login page. As a general rule in this case you should
+     * also implement the loginpage_hook as well.
+     *
+     */
+    function pre_loginpage_hook() {
+        // override if needed, eg by redirecting to an external login page
+        // or logging in a user:
+        // complete_user_login($user);
+    }
+
     /**
      * Post authentication hook.
      * This method is called from authenticate_user_login() for all enabled auth plugins.
diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 7b74a701dff..b80bb302ce9 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -2902,8 +2902,22 @@ function require_login($courseorid = null, $autologinguest = true, $cm = null, $
             if (!empty($_SERVER['HTTP_REFERER'])) {
                 $SESSION->fromurl  = $_SERVER['HTTP_REFERER'];
             }
-            redirect(get_login_url());
-            exit; // Never reached.
+
+            // Give auth plugins an opportunity to authenticate or redirect to an external login page
+            $authsequence = get_enabled_auth_plugins(true); // auths, in sequence
+            foreach($authsequence as $authname) {
+                $authplugin = get_auth_plugin($authname);
+                $authplugin->pre_loginpage_hook();
+                if (isloggedin()) {
+                    break;
+                }
+            }
+
+            // If we're still not logged in then go to the login page
+            if (!isloggedin()) {
+                redirect(get_login_url());
+                exit; // Never reached.
+            }
         }
     }