Upload to S3 via CloudFront results in 403

Question

I'm trying to sign a URL to upload to S3 via CloudFront.

S3 has a bucket policy setup
CloudFront is using a custom domain/cert
CloudFront is configured to forward headers
Signed URLs for GET are working

If I sign a URL with a Policy:

https://staging.*SNIP*.io/341-a25e82ef-8210-49bc-9fbd-b3f0c4807080-original.jpg?Policy=*SNIP*&Signature=*SNIP*&Key-Pair-Id=*SNIP*

Or without the Policy but using an Expires

https://staging.*SNIP*.io/343-aa3e9a57-4d85-4c90-bf05-3d6fdac04a49-original.jpg?Expires=1457765627&Signature=*SNIP*&Key-Pair-Id=*SNIP*

I consistency get:

<Error>
    <Code>AccessDenied</Code>
    <Message>Query-string authentication requires the Signature, Expires and AWSAccessKeyId parameters</Message>
    <RequestId>*snip*</RequestId>
    <HostId>*snip*</HostId>
</Error>

I've rolled my own signing based on various different SO answers. I've tried using the built in signing from AWS SDK. I've destroyed and recreated the CloudFront distribution.

I've completely run out of ideas to try.

I've probably looked at every single issue on SO about signed urls with cloudfront but nothing has helped. I cannot get past this 403 error.

Edit: Seems AWS has no idea why it's not working, it all appears to be configured correctly.

Phill Phill · Accepted Answer · 2016-03-21T16:38:46

I managed to figure this out. The documentation (at the time of writing this) confused me. Basically:

1) The Cloudfront Distribution needs to be set to restrict access to bucket. (If this isn't done it doesn't seem to pass the auth headers to S3)

2) Hash the payload

3) Sign the Cloudfront URL

4) Sign the request

To hash the payload I used Crypto.js (Core & SHA256)

var reader = new FileReader();

reader.onload = function(readerEvt) {
    var binaryString = readerEvt.target.result;
    var wordArray = arrayBufferToWordArray(binaryString);
    var hash = CryptoJS.SHA256(wordArray);

    var hashedPayload = hash.toString(CryptoJS.enc.Hex);

    // send the hashed payload serverside for use in calculating the signed request
};

reader.readAsArrayBuffer(file);

And to sign the request I followed:

http://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-header-based-auth.html

(comment if you need more information)

Upload to S3 via CloudFront results in 403

1 Answers