# Get started with Ash Authentication

If you haven't already, read [the getting started guide for
Ash](https://ash-hq.org/docs/guides/ash/latest/tutorials/get-started.md). This
assumes that you already have resources set up, and only gives you the steps to
add authentication to your resources and APIs.

## Add to your application's dependencies

Bring in the `ash_authentication` dependency:

```elixir
# mix.exs

defp deps()
  [
    # ...
    {:ash_authentication, "~> 4.0"}
  ]
end
```

And add `ash_authentication` to your `.formatter.exs`:

```elixir
# .formatter.exs
[
  import_deps: [..., :ash_authentication]
]
```

## Choosing your extensions, strategies and add-ons

Ash Authentication supports many different features, each configured separately.

### `AshAuthentication`

This is the core extension, and is required. It provides main DSL for working
with authentication and related features and should be added to your "user"
resource.

The `AshAuthentication` extension provides configuration and sensible defaults for settings which relate to authentication, regardless of authentication mechanism.

All strategy and add-on configuration is nested inside this DSL block.

It will define a `get_by_subject_name` read action on your resource, which is
used when converting tokens or session information into a resource record.

### `AshAuthentication.Strategy.Password`

This authentication strategy provides registration and sign-in for users using a local
identifier (eg `username`, `email` or `phone_number`) and a password. It will
define register and sign-in actions on your "user" resource. You are welcome to
define either or both of these actions yourself if you wish to customise them -
if you do so then the extension will do its best to validate that all required
configuration is present.

The `AshAuthentication.Strategy.Password` DSL allows you to override any of the default values.

### `AshAuthentication.Strategy.OAuth2`

This authentication strategy provides registration and sign-in for users using a
remote [OAuth 2.0](https://oauth.net/2/) server as the source of truth. You
will be required to provide either a "register" or a "sign-in" action depending
on your configuration, which the strategy will attempt to validate for common
misconfigurations.

### `AshAuthentication.AddOn.Confirmation`

This add-on allows you to confirm changes to a user record by generating and
sending them a confirmation token which they must submit before allowing the
change to take place.

### `AshAuthentication.TokenResource`

This extension allows you to easily create a resource which will store
information about tokens that can't be encoded into the tokens themselves. A
resource with this extension must be present if token generation is enabled.

### `AshAuthentication.UserIdentity`

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.

## Example

Let's create an `Accounts` domain in our application which provides a `User`
resource and a `Token` resource.

First, let's define our domain:

```elixir
# lib/my_app/accounts.ex

defmodule MyApp.Accounts do
  use Ash.Domain

  resources do
    resource MyApp.Accounts.User
    resource MyApp.Accounts.Token
  end
end
```

Be sure to add it to the `ash_domains` config in your `config.exs`

```elixir
# in config/config.exs
config :my_app, ash_domains: [..., MyApp.Accounts]
```

Next, let's define our `Token` resource. This resource is needed
if token generation is enabled for any resources in your application. Most of
the contents are auto-generated, so we just need to provide the data layer
configuration and the API to use.

But before we do, we need to install a postgres extension.

```elixir
# lib/my_app/repo.ex

defmodule MyApp.Repo do
  use AshPostgres.Repo, otp_app: :my_app

  def installed_extensions do
    ["ash-functions", "uuid-ossp", "citext"]
  end
end
```

You can skip this step if you don't want to use tokens, in which case remove the
`tokens` DSL section in the user resource below.

```elixir
# lib/my_app/accounts/token.ex

defmodule MyApp.Accounts.Token do
  use Ash.Resource,
    data_layer: AshPostgres.DataLayer,
    extensions: [AshAuthentication.TokenResource],
    # If using policies, enable the policy authorizer:
    # authorizers: [Ash.Policy.Authorizer],
    domain: MyApp.Accounts

  postgres do
    table "tokens"
    repo MyApp.Repo
  end

  # If using policies, add the following bypass:
  # policies do
  #   bypass AshAuthentication.Checks.AshAuthenticationInteraction do
  #     authorize_if always()
  #   end
  # end
end
```

Lastly let's define our `User` resource, using password authentication and token
generation enabled.

```elixir
# lib/my_app/accounts/user.ex

defmodule MyApp.Accounts.User do
  use Ash.Resource,
    data_layer: AshPostgres.DataLayer,
    extensions: [AshAuthentication],
    authorizers: [Ash.Policy.Authorizer],
    domain: MyApp.Accounts

  attributes do
    uuid_primary_key :id
    attribute :email, :ci_string, allow_nil?: false, public?: true
    attribute :hashed_password, :string, allow_nil?: false, sensitive?: true
  end

  authentication do
    strategies do
      password :password do
        identity_field :email
      end
    end

    tokens do
      enabled? true
      token_resource MyApp.Accounts.Token
      signing_secret fn _, _ ->
        Application.fetch_env(:my_app, :token_signing_secret)
      end
    end
  end

  postgres do
    table "users"
    repo MyApp.Repo
  end

  identities do
    identity :unique_email, [:email]
  end

  # You can customize this if you wish, but this is a safe default that
  # only allows user data to be interacted with via AshAuthentication.
  policies do
    bypass AshAuthentication.Checks.AshAuthenticationInteraction do
      authorize_if always()
    end

    policy always() do
      forbid_if always()
    end
  end
end
```

Here we've added password authentication, using an email address as our
identifier.

Now we have enough in place to register and sign-in users using the
`AshAuthentication.Strategy` protocol.

## Token generation

If you have token generation enabled then you need to provide (at minimum) a
signing secret. As the name implies this should be a secret. AshAuthentication
provides a mechanism for looking up secrets at runtime using the
`AshAuthentication.Secret` behaviour. To save you a click, this means that you
can set your token signing secret using either a static string (please don't!),
a two-arity anonymous function, or a module which implements the
`AshAuthentication.Secret` behaviour.

At its simplest you should so something like this:

```elixir
# in lib/my_app/accounts/user.ex

signing_secret fn _, _ ->
  Application.fetch_env(:my_app, :token_signing_secret)
end
```

Then, specify the secret token in the config file:

```elixir
# in config/config.exs
config :my_app, :token_signing_secret, "some_super_secret_random_value"
```

> ### The signing secret must not be committed to source control {: .warning}
>
> Proper management of secrets is outside the scope of this tutorial, but is
> absolutely crucial to the security of your application.

## Plugs and routing

If you're using Phoenix, then you can skip this section and go straight to
[Integrating Ash Authentication and Phoenix](https://ash-hq.org/docs/guides/ash_authentication_phoenix/latest/tutorials/getting-started-with-ash-authentication-phoenix)

In order for your users to be able to sign in, you will likely need to provide
an HTTP endpoint to submit credentials or OAuth requests to. Ash Authentication
provides `AshAuthentication.Plug` for this purposes. It provides a `use` macro
which handles routing of requests to the correct providers, and defines
callbacks for successful and unsuccessful outcomes.

Let's generate our plug:

```elixir
# lib/my_app/auth_plug.ex

defmodule MyApp.AuthPlug do
  use AshAuthentication.Plug, otp_app: :my_app

  def handle_success(conn, _activity, user, token) do
    if is_api_request?(conn) do
      conn
      |> send_resp(200, Jason.encode!(%{
        authentication: %{
          success: true,
          token: token
        }
      }))
    else
      conn
      |> store_in_session(user)
      |> send_resp(200, EEx.eval_string("""
      <h2>Welcome back <%= @user.email %></h2>
      """, user: user))
    end
  end

  def handle_failure(conn, _activity, _reason) do
    if is_api_request?(conn) do
      conn
      |> send_resp(401, Jason.encode!(%{
        authentication: %{
          success: false
        }
      }))
    else
      conn
      |> send_resp(401, "<h2>Incorrect email or password</h2>")
    end
  end

  defp is_api_request?(conn), do: "application/json" in get_req_header(conn, "accept")
end
```

Now that this is done, you can forward HTTP requests to it from your app's main
router using `forward "/auth", to: MyApp.AuthPlug` or similar.

Your generated auth plug module will also contain `load_from_session` and
`load_from_bearer` function plugs, which can be used to load users into assigns
based on the contents of the session store or `Authorization` header.

## Supervisor

AshAuthentication includes a supervisor which you should add to your
application's supervisor tree. This is used to run any periodic jobs related to
your authenticated resources (removing expired tokens, for example).

### Example

```elixir
defmodule MyApp.Application do
  use Application

  def start(_type, _args) do
    children = [
      # ...
      # add this line -->
      {AshAuthentication.Supervisor, otp_app: :my_app}
      # <-- add this line
    ]
    # ...
  end
end
```

## Summary

In this guide we've learned how to install Ash Authentication, configure
resources and handle authentication HTTP requests.

You should now have an Ash application with working user authentication.

Up next, [Using with Phoenix](https://ash-hq.org/docs/guides/ash_authentication_phoenix/latest/tutorials/getting-started-with-ash-authentication-phoenix).