gistfile1.txt

  var PREFIX_NAME = "identity.mozilla.com/picl/v1/";
  var bitSlice = sjcl.bitArray.bitSlice;
  
  function deriveHawkCredentials(tokenHex, context, size) {
    var token = sjcl.codec.hex.toBits(tokenHex);
    var info = sjcl.codec.utf8String.toBits(PREFIX_NAME + context);

    return hkdf(token, info, undefined, size || 3 * 32)
      .then(function(out) {
        var authKey = bitSlice(out, 8 * 32, 8 * 64);
        var bundleKey = bitSlice(out, 8 * 64);

        return {
          algorithm: "sha256",
          id: sjcl.codec.hex.fromBits(bitSlice(out, 0, 8 * 32)),
          key: authKey,
          bundleKey: bundleKey
        };
      });
  }