How to use AWS.CloudFront.Signer in Lambda function

Question

I'm trying to use Lambda to generate and return a signed cookie so my iOS app can use the cookie to access restricted files via CloudFront.

I think this should be possible using the Signer class: http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/CloudFront/Signer.html

On this basis I have written the following Lambda function:

var AWS = require('aws-sdk');
var keyPairId = 'APK...';
var privateKey = 'MIIE...';
var signer = new AWS.CloudFront.Signer(keyPairId, privateKey);

exports.handler = function(event, context) {
    var options = {url: "https://xxxxxx.cloudfront.net", expires: 1357100000};

    signer.getSignedCookie(options, function(err, data) {
        if (err) {
            context.fail(err);
        } else {
            context.succeed('Success');
        }
    });
};

However, this does not work. I keep getting the error 'Process exited before completing request'. I have tried many permutations for the format of the 'options' parameter, none of which make any difference.

Any help would be appreciated.

Answer 1

It turns out my private key format was incorrect. It needs to include the '-----BEGIN RSA PRIVATE KEY-----' wording and also the new line characters, like this (private key mangled for obvious reasons):

var privateKey = '-----BEGIN RSA PRIVATE KEY-----' + '\n' +
'MIIEogIBAAKCAQEAgaqMPqZ2QlhLx7pmguBMR32+dLPq7HrXN92z+QLbLgQklDpU' + '\n' +
'D/LLayMk5tyoZXLjRElZiWgIbLa8ftCQBVT1feG9XbwJVvBKqBkZzHR7xB47LVud' + '\n' +
't8zatnHHQngXkFV/YY+RAv9XN3E6GacXn02cGKbF14pQWFbjdJDcqUq1yf8/b9i7' + '\n' +
'JorOYYarXYXXYPaRp1HxSDAZkjM5WC0GeOk7v4cCgYB5chK6CARv5Wx9yzVYurvQ' + '\n' +
'KJxpidxV2AE4MgTkg8UeK7GPhizJIIKRPmvfM/rmiRC9NvrCHzTsVwk0mVWDhRuH' + '\n' +
'iATROrmPVQA6CZYODAmjXXXXXXsREg2s4+6XKzH/Cylb1YTowkIkWNyZEAtuyaBK' + '\n' +
'BBswVdO8VlOKQoouH71ktQKBgF1Sr4/btRI2wiVWWnEaORJO6+3Pekm4xyIbaOPo' + '\n' +
'yaRSy3KOQETUUR9Wg6dEwCEXBkBfte1dk/DIzES7FppypeXqu7viRLmOC1gXEK+6' + '\n' +
'k1hwClaKGhqafVVsHSsUzIUkBusoo4GKTXnrl/EPD5gpgt9TsPt/D1KqWW5sxfrl' + '\n' +
'dm+fAoGAcr0QqHdGea5OeC0fQGFZkgSQZ3ojdX43KWXXr5Jl+4ZiJTbOYqgGE+DL' + '\n' +
'QJX1I9fqruHhn02hXXX+eTOLOT4GDv2Lf6uHhQPHWgv4K3u/7Xb35Pumn/x2e8vb' + '\n' +
'xrRsk3KxdYAq+I9mpjYKIZL2EswnIkOTFJR+3O179/vpsFpIACg=' + '\n' +
'-----END RSA PRIVATE KEY-----';

With this change everything works fine.