knplabs/knpbundles — comment on commit 5c726c35c0bde0abc7f82833f9ebb704e8bdb8c9
File: src/Knp/Bundle/KnpBundlesBundle/Entity/KnpbundlesUser.php line 34
By torchello:

We can add later other OAuth provider. So this field is required when users with similar names are logged via different OAuth providers. And we can use this somehow on site (display oauth provider icon near username...)