frenzy/lib/frenzy_web/controllers/fervor/oauth_controller.ex

defmodule FrenzyWeb.Fervor.OauthController do
  use FrenzyWeb, :controller
  alias Frenzy.{Repo, FervorClient, User, ApprovedClient}
  alias FrenzyWeb.Endpoint

  def authorize_get(conn, params) do
    user_token = get_session(conn, :user_token)

    case Phoenix.Token.verify(Endpoint, "user token", user_token, max_age: 24 * 60 * 60) do
      {:error, _reason} ->
        continue = "#{conn.request_path}?#{conn.query_string}"
        redirect(conn, to: Routes.login_path(Endpoint, :login, continue: continue))

      {:ok, user_id} ->
        case Repo.get(User, user_id) do
          nil ->
            continue = "#{conn.request_path}?#{conn.query_string}"
            redirect(conn, to: Routes.login_path(Endpoint, :login, continue: continue))

          user ->
            conn
            |> assign(:user, user)
            |> try_render_authorize(params)
        end
    end
  end

  def try_render_authorize(
        conn,
        %{
          "response_type" => "code",
          "client_id" => client_id,
          "redirect_uri" => redirect_uri
        } = params
      ) do
    case Repo.get_by(FervorClient, client_id: client_id) do
      nil ->
        conn

      client ->
        if redirect_uri == client.redirect_uri do
          render(conn, "authorize.html", %{
            client: client,
            state: Map.get(params, "state")
          })
        else
          conn
          |> put_status(400)
          |> json(%{error: "mismatched redirect uri"})
        end
    end
  end

  def try_render_authorize(conn, _params) do
    conn
    |> put_status(400)
    |> json(%{error: "invalid parameters"})
  end

  def authorize_post(conn, params) do
    user_token = get_session(conn, :user_token)

    case Phoenix.Token.verify(Endpoint, "user token", user_token, max_age: 24 * 60 * 60) do
      {:error, _reason} ->
        continue = "#{conn.request_path}?#{conn.query_string}"
        redirect(conn, to: Routes.login_path(Endpoint, :login, continue: continue))

      {:ok, user_id} ->
        case Repo.get(User, user_id) do
          nil ->
            continue = "#{conn.request_path}?#{conn.query_string}"
            redirect(conn, to: Routes.login_path(Endpoint, :login, continue: continue))

          user ->
            conn
            |> assign(:user, user)
            |> try_authorize(params)
        end
    end
  end

  def try_authorize(conn, %{"client_id" => client_id} = params) do
    user = conn.assigns[:user]
    client = Repo.get_by(FervorClient, client_id: client_id)

    state = Map.get(params, "state")

    auth_code = :crypto.strong_rand_bytes(32) |> Base.url_encode64(padding: false)

    changeset =
      Ecto.build_assoc(user, :approved_clients, %{
        auth_code: auth_code,
        client_id: client_id
      })

    {:ok, _approved_client} = Repo.insert(changeset)

    case client.redirect_uri do
      "urn:ietf:wg:oauth:2.0:oob" ->
        render(conn, "successfully_authorized.html", %{
          auth_code: auth_code
        })

      redirect_uri ->
        parsed = URI.parse(redirect_uri)

        query =
          URI.encode_query(
            if state, do: %{code: auth_code, state: state}, else: %{code: auth_code}
          )

        uri = %URI{parsed | query: query}
        redirect(conn, to: uri)
    end
  end

  def try_authorize(conn, _params) do
    conn
    |> put_status(400)
    |> json(%{error: "invalid parameters"})
  end

  def token(
        conn,
        %{
          "redirect_uri" => redirect_uri,
          "client_id" => client_id,
          "client_secret" => client_secret
        } = params
      ) do
    case Repo.get_by(FervorClient, client_id: client_id) do
      nil ->
        conn
        |> put_status(401)
        |> json(%{error: "invalid_client", error_description: "incorrect client information"})

      client ->
        if client_secret == client.client_secret and redirect_uri == client.redirect_uri do
          conn
          |> assign(:client, client)
          |> try_generate_token(params)
        else
          conn
          |> put_status(400)
          |> json(%{error: "invalid_grant", error_description: "incorrect client information"})
        end
    end
  end

  def token(conn, _params) do
    json(conn, %{error: "invalid_request", error_description: "missing parameters"})
  end

  def try_generate_token(conn, %{
        "grant_type" => "authorization_code",
        "authorization_code" => auth_code
      }) do
    case Repo.get_by(ApprovedClient, auth_code: auth_code) do
      nil ->
        conn
        |> put_status(400)
        |> json(%{error: "invalid_grant", error_description: "invalid authorization code"})

      approved_client ->
        access_token = :crypto.strong_rand_bytes(32) |> Base.url_encode64(padding: false)

        changeset =
          ApprovedClient.changeset(approved_client, %{
            auth_code: nil,
            access_token: access_token
          })

        {:ok, _approved_client} = Repo.update(changeset)

        json(conn, %{
          access_token: access_token,
          token_type: "bearer"
        })
    end
  end

  def try_generate_token(conn, _params) do
    conn
    |> put_status(400)
    |> json(%{
      error: "unsupported_grant_type",
      error_description: "only grant_type=authorization_code is supported"
    })
  end
end