apa-api/src/domain/services/RequestSigner.coffee

Amazon Product Advertising API client

_ = require 'lodash'
URI = require 'URIjs'
crypto = require 'crypto'

class RequestSigner
  sign: (request) ->
    am = request.apiMeta
    params = request.asParams()
    normalized = normalize(params)
    source = prefix(am).concat([normalized]).join('\n')
    signature = digest(source, request.credential)

    "#{am.protocol}://#{am.endPoint}#{am.uri}?#{normalized}&Signature=#{signature}"

module.exports = RequestSigner

##################
# PRIVATE
##################
normalize = (params) ->
  encoded = _.map params, (value, key) ->
    [escape(key), escape(value)].join('=')
  encoded.sort().join('&')

prefix = (apiMeta) ->
  [
    apiMeta.method
    apiMeta.endPoint
    apiMeta.uri
  ]

escape = (value) ->
  URI.encode(value)

digest = (source, credential) ->
  hmac = crypto.createHmac('sha256', credential.secretKey)
  hmac.update(source)
  escape hmac.digest('base64')