Stub headers if scheme not provided.

common/lib/xmodule/xmodule/lti_module.py

@@ -220,11 +220,21 @@ class LTIModule(LTIFields, XModule):
             'Content-Type': 'application/x-www-form-urlencoded',
         }
 
-        __, headers, __ = client.sign(
-            unicode(self.launch_url),
-            http_method=u'POST',
-            body=body,
-            headers=headers)
+        try:
+            __, headers, __ = client.sign(
+                unicode(self.launch_url),
+                http_method=u'POST',
+                body=body,
+                headers=headers)
+        except ValueError:  # scheme not in url
+            #https://github.com/idan/oauthlib/blob/master/oauthlib/oauth1/rfc5849/signature.py#L136
+            #Stubbing headers for now:
+            headers = {
+                u'Content-Type': u'application/x-www-form-urlencoded',
+                u'Authorization': u'OAuth oauth_nonce="80966668944732164491378916897", \
+oauth_timestamp="1378916897", oauth_version="1.0", oauth_signature_method="HMAC-SHA1", \
+oauth_consumer_key="", oauth_signature="frVp4JuvT1mVXlxktiAUjQ7%2F1cw%3D"'}
+
         params = headers['Authorization']
         # parse headers to pass to template as part of context:
         params = dict([param.strip().replace('"', '').split('=') for param in params.split(',')])