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messenger_bot

1.0.0-beta2
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Unofficial Facebook Messenger Platform chatbot client and webhook handler

Retired package: Deprecated
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messenger_bot lib messenger_bot plugs authenticate.ex
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lib/messenger_bot/plugs/authenticate.ex 

defmodule MessengerBot.Plug.Authenticate do

  @moduledoc """

  MessengerBot plug implementation to verify the sha1 signature with request body.

  """



  import Plug.Conn

  alias Plug.Conn

  alias MessengerBot.Config

  alias :crypto, as: Crypto



  @doc false

  def init(opts) do

    opts

  end



  @doc false

  def call(%{method: "POST"} = conn, _opts) do

    {:ok, body, _} = Conn.read_body(conn)

    conn = put_private(conn, :body, body)

    case Conn.get_req_header(conn, "x-hub-signature") do

      ["sha1=" <> signature] ->

        expected_signature = calculate_request_signature(body)

        case signature == expected_signature do

          true -> conn

          false -> err_resp(conn, :unauthorized, %{"signature" => "invalid"})

        end

      _ ->

        err_resp(conn, :unauthorized, %{"signature" => "required"})

    end

  end

  def call(conn, _),

    do: conn



  defp calculate_request_signature(body) do

    :sha

    |> Crypto.hmac(Config.app_token(), body)

    |> Base.encode16()

    |> String.downcase()

  end



  defp err_resp(conn, status, errors) do

    conn

    |> put_resp_content_type("application/json")

    |> send_resp(status, :jiffy.encode(%{errors: errors}))

    |> halt()

  end

end