Example of doing base64 encoding in a JavaScript for an Apigee policy

exampleBase64Apigee.js

// exampleBase64.js
//
// for use within an Apigee JavaScript callout.
//
// Dino Chiesa, DChiesa@apigee.com
//
// Tuesday, 14 January 2014, 22:03
// ------------------------------------------------------------------


function trim(s) {
  return s.replace(/^\s\s*/, '').replace(/\s\s*$/, '');
}


// function b64decode (input) {
//     // Takes a base 64 encoded string "input", strips any "=" or
//     // "==" padding off it and converts its base 64 numerals into
//     // regular integers (using a string as a lookup table). These
//     // are then written out as 6-bit binary numbers and concatenated
//     // together. The result is split into 8-bit sequences and these
//     // are converted to string characters, which are concatenated
//     // and output.
// 
//     // The index/character relationship in the following string acts
//     // as a lookup table to convert from base 64 numerals to
//     // JavaScript integers.
//     var swaps = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
//         ob = "", output = "", tb = "", i, L;
// 
//     input = trim(input);
//     input = input.replace("=",""); // strip padding
// 
//     for (i=0, L = input.length; i < L; i++) {
//         tb = swaps.indexOf(input.charAt(i)).toString(2);
//         while (tb.length < 6) {
//             // Add significant zeroes
//             tb = "0"+tb;
//         }
//         while (tb.length > 6) {
//             // Remove significant bits
//             tb = tb.substring(1);
//         }
//         ob += tb;
//         while (ob.length >= 8) {
//             output += String.fromCharCode(parseInt(ob.substring(0,8),2));
//             ob = ob.substring(8);
//         }
//     }
// 
//     return output;
// }

function b64encode (input) {
  // Converts each character in the input to its Unicode number,
  // then writes out the Unicode numbers in binary, one after
  // another, into a string.  This string is then split up at
  // every 6th character, these substrings are then converted back
  // into binary integers and are used to subscript the "swaps"
  // array.  Since this would create HUGE strings of 1s and 0s,
  // the distinct steps above are actually interleaved in the code
  // below (ie. the long binary string, called "input_binary",
  // gets processed while it is still being created, so that it
  // never gets too big (in fact, it stays under 13 characters
  // long no matter what).

  // The indices of this array provide the map from numbers to
  // base64.
  var swaps = ["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","+","/"],

      tb, ib = "",
      output = "",
      i, L;

  for (i=0, L = input.length; i < L; i++) {
    // Turn the next character of input into astring of 8-bit binary
    tb = input.charCodeAt(i).toString(2);
    while (tb.length < 8) {
      tb = "0"+tb;
    }
    // Stick this string on the end of the previous 8-bit binary
    // strings to get one big concatenated binary representation
    ib = ib + tb;
    // Remove all 6-bit sequences from the start of the
    // concatenated binary string, convert them to a base 64
    // character and append to output.  Doing this here prevents
    // ib from getting massive
    while (ib.length >= 6) {
      output = output + swaps[parseInt(ib.substring(0,6),2)];
      ib = ib.substring(6);
    }
  }
  // Handle any necessary padding
  if (ib.length == 4) {
    tb = ib + "00";
    output += swaps[parseInt(tb,2)] + "=";
  }
  if (ib.length == 2) {
    tb = ib + "0000";
    output += swaps[parseInt(tb,2)] + "==";
  }
  return output;
}


var user = context.getVariable("myvariable.user"),
   pwd = context.getVariable("myvariable.pwd"),
   b64blob = b64encode(user + ':' + pwd);

context.setVariable("request.header.Authorization", 'Basic ' + b64blob);

Dino, I get an error Javascript runtime error: "TypeError: Cannot call method "replace" of null

on the decode