Improved session auth module routing.

modules/auth/cms_authentication_module.e

@@ -1,7 +1,7 @@
 note
 	description: "Module Auth"
-	date: "$Date$"
-	revision: "$Revision$"
+	date: "$Date: 2016-04-13 10:59:18 +0200 (mer., 13 avr. 2016) $"
+	revision: "$Revision: 98616 $"
 
 class
 	CMS_AUTHENTICATION_MODULE
@@ -159,7 +159,7 @@ feature -- Hooks configuration
 				l_url_name := "site_sign_in_url"
 				l_url := a_response.url (roc_login_location, Void)
 			end
-			if l_destination /= Void then
+			if l_destination /= Void and then not l_url.has_substring ("?destination") then
 				l_url.append ("?destination=" + percent_encoded (l_destination))
 			end
 			a_value.force (l_url, l_url_name)