Handle when error_description isn't present in www-authenticate header

HISTORY.rst

@@ -3,6 +3,10 @@
 History
 -------
 
+pending
+=======
+* Fix bug in ``contrib.drf.OIDCAuthentication`` where ``error_description`` is assumed to be present in ``www-authenticate`` header despite it being optional in the spec.
+
 2.0.0 (2021-07-27)
 ==================
 

mozilla_django_oidc/contrib/drf.py

@@ -86,7 +86,7 @@ def authenticate(self, request):
             # we can get from the www-authentication header) in the response.
             if resp.status_code == 401 and "www-authenticate" in resp.headers:
                 data = parse_www_authenticate_header(resp.headers["www-authenticate"])
-                raise exceptions.AuthenticationFailed(data["error_description"])
+                raise exceptions.AuthenticationFailed(data.get("error_description", "no error description in www-authenticate"))
 
             # for all other http errors, just re-raise the exception.
             raise