support optional GET parameters for end_session_endpoint

Author: bmauser

src/OpenIDConnectClient.php

@@ -427,12 +427,13 @@ public function authenticate(): bool
      *
      * @param string $idToken ID token (obtained at login)
      * @param string|null $redirect URL to which the RP is requesting that the End-User's User Agent
+     * @param array $params Optional GET parameters to end-session endpoint
      * be redirected after a logout has been performed. The value MUST have been previously
      * registered with the OP. Value can be null.
      *
      * @throws OpenIDConnectClientException
      */
-    public function signOut(string $idToken, $redirect) {
+    public function signOut(string $idToken, $redirect, array $params = []) {
         $sign_out_endpoint = $this->getProviderConfigValue('end_session_endpoint');
 
         if($redirect === null){
@@ -444,6 +445,9 @@ public function signOut(string $idToken, $redirect) {
                 'post_logout_redirect_uri' => $redirect];
         }
 
+        if($params)
+            $signout_params = array_merge($signout_params, $params);
+
         $sign_out_endpoint  .= (strpos($sign_out_endpoint, '?') === false ? '?' : '&') . http_build_query( $signout_params, '', '&', $this->encType);
         $this->redirect($sign_out_endpoint);
     }