Enable support in OIDC for endpoints without user info support

The user info endpoint is apparently optional.

util/config/validators/test/test_validate_oidc.py

@@ -27,7 +27,7 @@ def test_validate_oidc_login(app):
   def handler(_, __):
     url_hit[0] = True
     data = {
-      'userinfo_endpoint': 'foobar',
+      'token_endpoint': 'foobar',
     }
     return {'status_code': 200, 'content': json.dumps(data)}