make_paapi_sig.js

/*
Based on:
http://lastoneofthezodiac.blog38.fc2.com/blog-entry-5613.html

Needs sha_256.js <http://point-at-infinity.org/jssha256/> like following:
<script type="text/javascript" src="./jssha256.js"></script>
*/

function pad0(n, len, radix) {
  radix = radix || 10;
  var s = '00000000000' + n.toString(radix);
  return s.substr(s.length - len, len);
}

function make_timestamp() {
  var d = new Date();
  return  [ d.getUTCFullYear(), '-',
            pad0(d.getUTCMonth() + 1, 2), '-',
            pad0(d.getUTCDate(), 2),
            'T',
            pad0(d.getUTCHours(), 2), '%3A',	// %3A == ':'
            pad0(d.getUTCMinutes(), 2), '%3A',
            pad0(d.getUTCSeconds(), 2),
            'Z'
          ].join('');
}

function pad_align(str, padstr, align) {
  var len = str.length;
  var mod = len % align;
  return mod == 0 ? str : str + padstr.substr(0, align - mod);
}

var base64_table = [
  'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
  'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
  'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
  't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',
  '8', '9', '+', '/' ];

function array_base64(ary) {
  var bit_ary = [];
  for(var i = 0 ; i < ary.length ; i++) {
    bit_ary.push(pad0(ary[i], 8, 2));
  }
  var bit_str = bit_ary.join('');
  bit_str = pad_align(bit_str, '00000', 6);
  var encoded_ary = [];
  for(i = 0 ; i < bit_str.length ; i += 6) {
    var n = parseInt(bit_str.substr(i, 6), 2);
    encoded_ary.push(base64_table[n]);
  }
  return pad_align(encoded_ary.join(''), '===', 4);
}

function make_hmac_sha256(str, skey) {
  HMAC_SHA256_init(skey);
  HMAC_SHA256_write(str);
  var mac_ary = HMAC_SHA256_finalize();	// byte array

  return array_base64(mac_ary);
}

function make_signed_url(host, baseurl, param, skey) {
  var param_ary = param.split('&');
  var timestamp = 'Timestamp=' + make_timestamp();
  param_ary.push(timestamp);
  var param2 = "GET\n" + host + "\n" + baseurl + "\n" + 
               param_ary.sort().join('&');

  return [
    'http://', host, baseurl, '?', param, '&', timestamp, '&Signature=',
    encodeURIComponent(make_hmac_sha256(param2, skey))
  ].join('');
}