HMAC Authentication Plug

Plug support for HMAC authentication. This is used for authentication between server sides.

Installation

This package can be installed by adding plug_hmac_auth to your list of dependencies in mix.exs:

def deps do
  [
    {:plug_hmac_auth, "~> 0.1.0"}
  ]
end

Usage

Here we demonstrate the usage by this example. Replace the PlugHmacAuthExample by the name of your own web site.

PlugHmacAuthExampleWeb.Endpoint

We use some raw data as payload to verify the request from client.

For those GET requests, we use query string as payload.

For other requests, we use raw body as payload. But the raw body of request can only be read once. That means we can't read the raw body after the Plug.Parsers. Instead of the original body reader provided by Plug.Parsers, we need to use a custom body reader to cache the raw body.

plug Plug.Parsers,
  parsers: [:urlencoded, :multipart, :json],
  pass: ["*/*"],
  json_decoder: Phoenix.json_library(),
  body_reader: {PlugHmacAuth.BodyReader, :read_body, []}

PlugHmacAuthExampleWeb.Router

In the router module of your web site, define a new pipeline to enable the plug of HMAC authentication:

pipeline :plug_hmac_auth do
  plug(PlugHmacAuth,
    key_access_id: "x-access-id",
    key_signature: "x-access-signature",
    hmac_hash_algo: :sha512,
    secret_handler: PlugHmacAuthExample.Handlers.SecretHandler,
    error_handler: PlugHmacAuthExampleWeb.ErrorHandler
  )
end

Module PlugHmacAuth needs these options:

• key_access_id: The key of access_id in the HTTP request header.
• key_signature: The key of signature in the HTTP request header.
• hmac_hash_algo: The algorithm of HMAC.
• secret_handler: Secret handler is the module to get the secret by given access_id.
• error_handler: Error handler is the module to handle the unauthorized request.

HMAC hash algorithm

Here lists the algorithms current supported.

Secret Handler

We need to implement the callback function of get_secret_key/1 to let authenticator know how to get the secret key by given access id.

Error Handler

We need to implement the callback function of auth_error/2 to let the authenticator know how to handle the unauthorized request.

Documentation

See HexDocs.

Reference

• Demo API Server Using This HMAC Authentication Plug
• HMAC Authentication: Better protection for your API