As a user I become an admin if I use refresh token and set provider to admins.
And also I can get access token for the user if I use admin's refresh token and set provider to users.
{
"grant_type": "refresh_token",
"refresh_token": "{any_valid_refresh_token_for_the_user}",
"client_id": 1,
"client_secret": "secret",
"scope": "",
"provider": "admins"
}
Edit: Admin and User have the same id in database.