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Robust user authentication solution

Security advisory: This version has known vulnerabilities. View advisories
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pow lib pow plug message_verifier.ex
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lib/pow/plug/message_verifier.ex 

defmodule Pow.Plug.MessageVerifier do

  @moduledoc """

  This module can sign and verify messages.



  Based on `Phoenix.Token`.

  """

  alias Plug.{Conn, Crypto.KeyGenerator, Crypto.MessageVerifier}



  @callback sign(Conn.t(), binary(), binary(), keyword()) :: binary()

  @callback verify(Conn.t(), binary(), binary(), keyword()) :: {:ok, binary()} | :error



  @doc """

  Signs a message.



  `Plug.Crypto.MessageVerifier.sign/2` is used. The secret is derived from the

  `salt` and `conn.secret_key_base` using

  `Plug.Crypto.KeyGenerator.generate/3`. If `:key_generator_opts` is set in the

  config, this will be passed on to `Plug.Crypto.KeyGenerator`.

  """

  @spec sign(Conn.t(), binary(), binary(), keyword()) :: binary()

  def sign(conn, salt, message, config) do

    secret = derive(conn, salt, key_opts(config))



    MessageVerifier.sign(message, secret)

  end



  @doc """

  Verifies a message.



  `Plug.Crypto.MessageVerifier.sign/2` is used. The secret is derived from the

  `salt` and `conn.secret_key_base` using

  `Plug.Crypto.KeyGenerator.generate/3`. If `:key_generator_opts` is set in the

  config, this will be passed on to `Plug.Crypto.KeyGenerator`.

  """

  @spec verify(Conn.t(), binary(), binary(), keyword()) :: {:ok, binary()} | :error

  def verify(conn, salt, message, config) do

    secret = derive(conn, salt, key_opts(config))



    MessageVerifier.verify(message, secret)

  end



  defp derive(conn, key, key_opts) do

    conn.secret_key_base

    |> validate_secret_key_base()

    |> KeyGenerator.generate(key, key_opts)

  end



  defp validate_secret_key_base(nil),

    do: raise ArgumentError, "No conn.secret_key_base set"

  defp validate_secret_key_base(secret_key_base) when byte_size(secret_key_base) < 64,

    do: raise ArgumentError, "conn.secret_key_base has to be at least 64 bytes"

  defp validate_secret_key_base(secret_key_base), do: secret_key_base



  defp key_opts(config), do: Keyword.get(config, :key_generator_opts, [])

end