# `Ltix.AdvantageService`
[🔗](https://github.com/DecoyLex/ltix/blob/main/lib/ltix/advantage_service.ex#L1)

Behaviour for LTI Advantage service modules.

Each Advantage service implements this behaviour to describe its endpoint
type and required OAuth scopes. `Ltix.OAuth` uses these callbacks to
validate endpoints, derive scopes, and build authenticated clients,
without hardcoded knowledge of any specific service.

## Implementing a custom service

    defmodule MyApp.ProctorService do
      @behaviour Ltix.AdvantageService

      @impl true
      def endpoint_from_claims(%Ltix.LaunchClaims{} = _claims), do: :error

      @impl true
      def validate_endpoint(%MyApp.ProctorEndpoint{}), do: :ok

      def validate_endpoint(_),
        do: {:error, Ltix.Errors.Invalid.InvalidEndpoint.exception(service: __MODULE__)}

      @impl true
      def scopes(%MyApp.ProctorEndpoint{}),
        do: ["https://example.com/scope/proctoring"]
    end

# `endpoint_from_claims`

```elixir
@callback endpoint_from_claims(Ltix.LaunchClaims.t()) :: {:ok, term()} | :error
```

Extract the service's endpoint from launch claims.

# `scopes`

```elixir
@callback scopes(term()) :: [String.t()]
```

Return the OAuth scope URIs required by this endpoint.

# `validate_endpoint`

```elixir
@callback validate_endpoint(term()) :: :ok | {:error, Exception.t()}
```

Validate that the given value is a valid endpoint for this service.

---

*Consult [api-reference.md](api-reference.md) for complete listing*