ENT-619 Clean usernames coming from identity providers

Since we have started integrating with more clients, we have found that the usernames
that get passed are not compatible with our username restrictions. This PR introduces
a function to clean usernames to make them compatible, particularly in the auto registration
case.

common/djangoapps/third_party_auth/models.py

@@ -7,6 +7,7 @@ from __future__ import absolute_import
 
 import json
 import logging
+import re
 
 from config_models.models import ConfigurationModel, cache
 from django.conf import settings
@@ -65,6 +66,11 @@ def clean_json(value, of_type):
     return json.dumps(value_python, indent=4)
 
 
+def clean_username(username=''):
+    """ Simple helper method to ensure a username is compatible with our system requirements. """
+    return re.sub(r'[^-\w]+', '_', username)[:30]
+
+
 class AuthNotConfigured(SocialAuthBaseException):
     """ Exception when SAMLProviderData or other required info is missing """
     def __init__(self, provider_name):
@@ -259,7 +265,7 @@ class ProviderConfig(ConfigurationModel):
         # technically a data race between the creation of this value and the
         # creation of the user object, so it is still possible for users to get
         # an error on submit.
-        registration_form_data['username'] = pipeline_kwargs.get('username')
+        registration_form_data['username'] = clean_username(pipeline_kwargs.get('username') or '')
 
         # Any other values that are present in the details dict should be copied
         # into the registration form details. This may include details that do