# File lib/oauth2/mac_token.rb, line 61
    def header(verb, url)
      timestamp = Time.now.utc.to_i
      nonce = Digest::MD5.hexdigest([timestamp, SecureRandom.hex].join(':'))

      uri = URI.parse(url)

      raise(ArgumentError, "could not parse \"#{url}\" into URI") unless uri.is_a?(URI::HTTP)

      mac = signature(timestamp, nonce, verb, uri)

      "MAC id=\"#{token}\", ts=\"#{timestamp}\", nonce=\"#{nonce}\", mac=\"#{mac}\""
    end