Plug used inside the phoenix controller to extract the encoded credential from the `authorization` header

AuthHeaders.ex

defmodule MyApp.Plugs.AuthHeaders do
  import Plug.Conn
  import Phoenix.Controller
  require Logger

  @doc """
  This Plug extract the `authentication` header from the connnaction
  and extrac the tocken containing the credentials. If the header has
  ther correct format it calls the `validate` function otherwise it
  will return a 401 error.
  """
  def verify_user_authentication(conn) do
    case get_req_header(conn, "authorization") do
      [<<"Basic ", token::binary>>] -> validate(conn, token)
      _                             -> send_bad_request(conn)
    end
  end

  @doc """
  Validate does receive a connection and the credentials encoded in base64. it
  will call `decode_credentials` to exract the data and lookup for the user
  in the database. If the user is present it send a 201 with the user data,
  otherwise it will return an error.
  """
  defp validate(conn, token) do
    [email, password] = decode_credentials(token)
    user = FlycatcherPhoenix.User.authenticate(%{ "email" => email, "password" => password })

    if user do
      render conn, "show.json", data: user
    else
      send_bad_request(conn)
    end
  end

  defp send_bad_request(conn) do
    conn
    |> send_resp(401, Poison.encode!(%{error: "user not authorised"}))
    |> halt
  end

  @doc """
  This is an helper to extract the credentials from the token. The data decode
  is a string with the following format `email:password`. I will split the
  result and retun it in a list
  """
  defp decode_credentials(token) do
    token
    |> :base64.decode
    |> String.split(":")
  end
end