gistfile1.txt

require 'base64'
require 'openssl'

module PayNowWidgetUtils
  def generate_signed_form(access_key, aws_secret_key, form_params)
    form_params['accessKey'] = access_key

    # lexicographically sort the form parameters
    # and create the canonicalized string
    str_to_sign = ""
    form_params.keys.sort.each { |k| str_to_sign += "#{k}#{form_params[k]}" }

    # calculate signature of the above string
    digest = OpenSSL::Digest::Digest.new('sha1')
    hmac = OpenSSL::HMAC.digest(digest, aws_secret_key, str_to_sign)
    form_params['signature'] = Base64.encode64(hmac).chomp

    # construct the form
    signed_form =<<-STARTFORM
                 <form action="https://authorize.payments-sandbox.amazon.com/pba/paypipeline"
                       method="post">
                 STARTFORM

    form_params.each do |key, value|
      next unless key and value
      signed_form +=<<-"FORMELEM"
                     <input type="hidden" name="#{key}" value="#{value}" >
            FORMELEM
    end

    signed_form +=<<-ENDFORM
                     <input type="image"
                            src="https://authorize.payments-sandbox.amazon.com/pba/images/amazonPaymentsButton.jpg"
            border="0" >
                 </form>
            ENDFORM

    return signed_form
  end
end