Hmac request signing

hmac_request_signing.rb

require 'base64'
require 'openssl'
require 'cgi'

module HmacRequestSigning
  def inject_signature_header(headers, signature)
    headers['X-Hmac-Sha256'] = signature
    headers
  end

  def request_signature(request)
    request.headers['X_HMAC_SHA256']
  end

  def hmac_sha256(key, message)
    digest = OpenSSL::HMAC.digest('sha256', key, message)
    # chomp -- the base64 encoded version will have a newline at the end
    Base64.encode64(digest).chomp
  end

  def sign_params(verb, host, path, secret_key, params)
    hmac_sha256(secret_key, serialized_params(verb, host, path, params))
  end

  def serialized_params(verb, host, path, params)
    [ verb.to_s.upcase,
      host,
      path,
      canonicalize_params(params) ].join("\n")
  end

  def canonicalize_params(params)
    # Make sure we have string keys, otherwise the sort does not work
    params.keys.sort.map do |key|
      [CGI.escape(key.to_s), CGI.escape(params[key].to_s)].join('=')
    end.join('&')
  end
end