Please use AWS4-HMAC-SHA256.

[indicalabs]

error message from aws: The authorization mechanism you have provided is not supported. Please use AWS4-HMAC-SHA256.

I was able to create aws4 signature, but it looks like the plupload doesn't support it

[pszalko]

I think I have the same issue with AWS4-HMAC-SHA256. Policy signature calculated and validated according to AWS documentation, but it does not work with plUpload.

The response I see is:

The request signature we calculated does not match the signature you provided. Check your key and signing method.

[pszalko]

It looks like plUpload does support AWS4-HMAC-SHA256.

After some research and double check of the multipart_params I found out that if you mix:

• signature (SHA1) with x-amz-signature (SHA256)
• add AWSAccessKeyId

then AWS API silently switches to AWS Signature Version 2 (aka SHA1).

I suggest double checking parameters defined in your multipart_params value according to: https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-authentication-HTTPPOST.html and make sure you're not sending additional AWS params like AWSAccessKeyId or signature.

This gist helped me to find the root cause of my issue: https://gist.github.com/jaredcassidy/1fb6af1c46f7b45bfc23cee90fbe4a3a

Anyway, I think it's time to update plUpload documentation to AWS Signature Version 4, since version 2 is currently deprecated and it will stop working at June 24, 2019.

Hope this message will help someone save few hours of digging into plUpload and AWS API.