Add optional OIDC avatar fetching from the “picture” claim

[bookstack] / dev / api / responses / users-create.json

{
  "id": 1,
  "name": "Dan Brown",
  "email": "[email protected]",
  "created_at": "2022-02-03T16:27:55.000000Z",
  "updated_at": "2022-02-03T16:27:55.000000Z",
  "external_auth_id": "abc123456",
  "slug": "dan-brown",
  "last_activity_at": "2022-02-03T16:27:55.000000Z",
  "profile_url": "https://docs.example.com/user/dan-brown",
  "edit_url": "https://docs.example.com/settings/users/1",
  "avatar_url": "https://docs.example.com/uploads/images/user/2021-10/thumbs-50-50/profile-2021.jpg",
  "roles": [
    {
      "id": 1,
      "display_name": "Admin"
    }
  ]
}