Return accounts linked to identity providers

Example response

{
  "data": {
    "username_linked_accounts": [
      {
        "link_time": 1443124003,
        "preferred_username": "username@example.com",
        "provider_id": "cpanelid",
        "provider_protocol": "openid_connect",
        "subject_unique_identifier": "123456789012345678901",
        "username": "username"
      }
    ]
  },
  "metadata": {
    "command": "get_users_authn_linked_accounts",
    "reason": "OK",
    "result": 1,
    "version": 1
  }
}