separator is hard coded to "?", when in fact it may need to be an & because the redirect_uri may already contain URL parameters

Author: honestbleeps

oauth2_provider/views/mixins.py

@@ -155,9 +155,14 @@ def error_response(self, error, **kwargs):
         :param error: :attr:`OAuthToolkitError`
         """
         oauthlib_error = error.oauthlib_error
+
+        separator = '?'
+        if '?' in oauthlib_error.redirect_uri:
+            separator = '&'
+
         error_response = {
             'error': oauthlib_error,
-            'url': "{0}?{1}".format(oauthlib_error.redirect_uri, oauthlib_error.urlencoded)
+            'url': "{0}{1}{2}".format(oauthlib_error.redirect_uri, separator, oauthlib_error.urlencoded)
         }
         error_response.update(kwargs)