Adds invitation-token fields and validation to an application-owned schema.

Declare the invitation's identifier and add your own fields for what accepting it grants:

defmodule MyApp.Accounts.Invitation do
  use Ecto.Schema
  import Ecto.Changeset

  alias Ithibati.Schema.Identifier
  alias Ithibati.Schema.Invitation

  use Invitation, identifier: :email, format: Identifier.email_format()

  schema "invitations" do
    ithibati_invitation()

    field :role, Ecto.Enum, values: [:admin, :author]
    belongs_to :site, MyApp.Sites.Site

    timestamps(type: :utc_datetime_usec)
  end

  def changeset(invitation, attrs, opts \ []) do
    invitation
    |> invitation_changeset(attrs, opts)
    |> cast(attrs, [:role, :site_id])
    |> validate_required([:role, :site_id])
  end
end

The options match Ithibati.Schema.User: required :identifier, optional :format and :format_message, plus :constraint_name and :unique_index. On invitations, the index options refer to token_hash, not the identifier. Non-identifier options can be module attributes declared before use; explicit nil values are rejected.

The identifier field must match the configured account schema's identifier. That agreement is checked when Ithibati.Config.invitation_schema/0 reads the application configuration.

Call ithibati_invitation/0 inside the schema. The macro generates invitation_changeset/3 and __ithibati_invitation__/1; defining either yourself is rejected at compile time. Invitations covers the table, token index and acceptance transaction.