Add an option to ignore logout errors (#227)

* Fix deprecated logging method

* Add an option to ignore IDP logout errors

Author: maxbes

README.rst

@@ -140,6 +140,13 @@ For example::
   import saml2
   SAML_LOGOUT_REQUEST_PREFERRED_BINDING = saml2.BINDING_HTTP_POST
 
+Ignore Logout errors
+--------------------
+When logging out, a SAML IDP will return an error on invalid conditions, such as the IDP-side session being expired.
+Use the following setting to ignore these errors and perform a local Django logout nonetheless::
+
+  SAML_IGNORE_LOGOUT_ERRORS = True
+
 Signed Logout Request
 ------------------------
 Idp's like Okta require a signed logout response to validate and logout a user. Here's a sample config with all required SP/IDP settings::

djangosaml2/views.py

@@ -522,7 +522,7 @@ def do_logout_service(request, data, binding, config_loader_path=None, next_page
             response = client.parse_logout_request_response(data['SAMLResponse'], binding)
         except StatusError as e:
             response = None
-            logger.warn("Error logging out from remote provider: " + str(e))
+            logger.warning("Error logging out from remote provider: " + str(e))
         state.sync()
         return finish_logout(request, response, next_page=next_page)
 
@@ -561,7 +561,9 @@ def do_logout_service(request, data, binding, config_loader_path=None, next_page
 
 
 def finish_logout(request, response, next_page=None):
-    if response and response.status_ok():
+    if (getattr(settings, 'SAML_IGNORE_LOGOUT_ERRORS', False) or
+            (response and response.status_ok())):
+
         if next_page is None and hasattr(settings, 'LOGOUT_REDIRECT_URL'):
             next_page = settings.LOGOUT_REDIRECT_URL
         logger.debug('Performing django logout with a next_page of %s',