Show error message for echo_attributes when not logged in via SAML

This fixes issue #72

Author: knaperek

Diff for: djangosaml2/views.py

@@ -323,8 +323,12 @@ def echo_attributes(request,
     client = Saml2Client(conf, state_cache=state,
                          identity_cache=IdentityCache(request.session))
     subject_id = _get_subject_id(request.session)
-    identity = client.users.get_identity(subject_id,
-                                         check_not_on_or_after=False)
+    try:
+        identity = client.users.get_identity(subject_id,
+                                             check_not_on_or_after=False)
+    except AttributeError:
+        return HttpResponse("No active SAML identity found. Are you sure you have logged in via SAML?")
+
     return render(request, template, {'attributes': identity[0]})