use saml_sls filter

Author: jazzsequence

onelogin-saml-sso/php/settings.php

@@ -61,6 +61,7 @@
  * Allow saml_acs URL query variable to be customized.
  */
 $saml_acs = apply_filters( 'onelogin_saml_acs', 'saml_acs' );
+$saml_sls = apply_filters( 'onelogin_saml_acs', 'saml_sls' );
 $acs_endpoint = get_option( 'onelogin_saml_alternative_acs', false ) ? plugins_url( 'alternative_acs.php', dirname( __FILE__ ) ) : wp_login_url() . '?' . $saml_acs;
 
 $settings = array (
@@ -74,7 +75,7 @@
             'url' => $acs_endpoint
         ),
         'singleLogoutService' => array (
-            'url' => get_site_url().'/wp-login.php?saml_sls'
+            'url' => get_site_url( null, '/wp-login.php?' . $saml_sls )
         ),
         'NameIDFormat' => $opt['NameIDFormat'],
         'x509cert' => get_option('onelogin_saml_advanced_settings_sp_x509cert'),