An Ash extension which generates the default user identities resource.

If you plan to support multiple different strategies at once (eg giving your users the choice of more than one authentication provider, or signing them into multiple services simultaneously) then you will want to create a resource with this extension enabled. It is used to keep track of the links between your local user records and their many remote identities.

The user identities resource is used to store information returned by remote authentication strategies (such as those provided by OAuth2) and maps them to your user resource(s). This provides the following benefits:

1. A user can be signed in to multiple authentication strategies at once.
2. For those providers that support it, AshAuthentication can handle automatic refreshing of tokens.

Storage

User identities are expected to be relatively long-lived (although they're deleted on log out), so should probably be stored using a permanent data layer sush as ash_postgres.

Usage

There is no need to define any attributes, etc. The extension will generate them all for you. As there is no other use-case for this resource it's unlikely that you will need to customise it.

defmodule MyApp.Accounts.UserIdentity do
  use Ash.Resource,
    data_layer: AshPostgres.DataLayer,
    extensions: [AshAuthentication.UserIdentity],
    domain: MyApp.Accounts

  user_identity do
    user_resource MyApp.Accounts.User
  end

  postgres do
    table "user_identities"
    repo MyApp.Repo
  end
end

If you intend to operate with multiple user resources, you will need to define multiple user identity resources.