Add default launch url for lti.

common/lib/xmodule/xmodule/js/src/lti/lti.js

@@ -16,9 +16,9 @@ window.LTI = (function () {
 
         // If the Form's action attribute is set (i.e. we can perform a normal
         // submit), then we submit the form and make the frame shown.
-        if (form.attr('action')) {
+        if (form.attr('action') && form.attr('action') !== 'http://www.example.com') {
             form.submit();
-            element.find('.lti').addClass('rendered')
+            element.find('.lti').addClass('rendered');
         }
     }
 

common/lib/xmodule/xmodule/lti_module.py

@@ -38,9 +38,12 @@ class LTIFields(object):
         vbid=put_book_id_here
         book_location=page/put_page_number_here
 
+    Default non-empty url for `launch_url` is needed due to oauthlib demand (url scheme should be presented)::
+
+    https://github.com/idan/oauthlib/blob/master/oauthlib/oauth1/rfc5849/signature.py#L136
     """
     lti_id = String(help="Id of the tool", default='', scope=Scope.settings)
-    launch_url = String(help="URL of the tool", default='', scope=Scope.settings)
+    launch_url = String(help="URL of the tool", default='http://www.example.com', scope=Scope.settings)
     custom_parameters = List(help="Custom parameters (vbid, book_location, etc..)", scope=Scope.settings)
 
 
@@ -213,7 +216,6 @@ class LTIModule(LTIFields, XModule):
         body.update(custom_parameters)
 
         headers = {
-            'Host': self.system.HOSTNAME,
             # This is needed for body encoding:
             'Content-Type': 'application/x-www-form-urlencoded',
         }

lms/djangoapps/courseware/tests/test_lti.py

@@ -75,6 +75,6 @@ class TestLTI(BaseTestXmodule):
             'input_fields': self.correct_headers,
             'element_class': self.item_module.location.category,
             'element_id': self.item_module.location.html_id(),
-            'launch_url': '',  # default value
+            'launch_url': 'http://www.example.com',  # default value
         }
         self.assertDictEqual(generated_context, expected_context)