Properly link the logout url on imap login failures

plugins/sso/sso.php

@@ -75,7 +75,9 @@ class sso extends rcube_plugin
 
   function login_failed($args)
   {
-    echo('<h3>There has been a login error with the mail server. Please go back and try again.</h3>');
+    $this->load_config();
+    $sso_logout_url = rcmail::get_instance()->config->get('sso_logout_url');
+    echo('<h3>There has been a login error with the mail server. Please try <a href="' . $sso_logout_url . '">logging out</a> and logging in again.</h3>');
     exit;
   }