Browser-Based Uploads Using POST - ruby

Question

I'm trying to create a client side uploads using POST with Signature Version 4 of AWS.
According to the documents
When i'm generating the signature on the server side I get an exact match with AWS signature mentioned in this example page.
However when I use it to upload the page I get this error:
SignatureDoesNotMatchThe request signature we calculated does not match the signature you provided. Check your key and signing method
This is the code I've used:
OpenSSL::HMAC.hexdigest('sha256', signing_key(string_to_sign), string_to_sign)
# step 2 in the aws documentation
def signing_key(encoded_policy)
# generate the correct date
date = extract_encoded_policy_date(encoded_policy)
date = time_adjust(date)
# encode all the fields by the algorithm
date_key = OpenSSL::HMAC.digest('sha256',"AWS4#{#secret_access_key}", date.strftime("%Y%m%d"))
date_region_key = OpenSSL::HMAC.digest('sha256',date_key, #region)
date_region_service_key = OpenSSL::HMAC.digest('sha256',date_region_key, #service)
signing_key = OpenSSL::HMAC.digest('sha256',date_region_service_key, 'aws4_request')
signing_key
end
def time_adjust(date)
time = Time.parse(date)
time += time.utc_offset
time.utc
end
After a little search in the net, i've encountered this article. Iv'e implemented this code and the upload succeeded.
signature = OpenSSL::HMAC.digest( OpenSSL::Digest::Digest.new('sha1'), #secret_access_key, string_to_sign)
Base64.encode64(signature).gsub("\n","")```
This is a small Demo for the client side code.
here is some literature I've found useful:
General description
Some code snippets from AWS
What is the differences between the two?
How can I get the first option to work and upload my files?
Is the example in the AWS page no longer valid?

Answer 1

After a research and comparing the AWS post example i found out that there were some redundant fields in the form that made AWS think i'm using SHA1.
After removing the AWSAccessKeyId field from the form and renaming some other fields I managed to make the AWS4 work.
This is the updated Demo
<form id="myForm" action="http://yourbucket.s3.amazonaws.com/" method="post" enctype="multipart/form-data">
<input type="hidden" id="key" name="key" value="uploads/${filename}"/>
<input type="hidden" id="acl" name="acl" value="YOUR_ACL_OPTION"/>
<input type="hidden" name="success_action_redirect" value="http://google.com" />
<input type="hidden" id="type" name="Content-Type" value="MIME_TYPE"/>
<input type="hidden" name="x-amz-meta-uuid" value="14365123651274" />
<input type="hidden" name="X-Amz-Credential" value="YOUR_CREDENTIALS" />
<input type="hidden" name="X-Amz-Algorithm" value="AWS4-HMAC-SHA256" />
<input type="hidden" id="date" name="X-Amz-Date" value="" />
<input type="hidden" name="x-amz-meta-tag" value="" />
<input type="hidden" id="policy" name="Policy" value="YOUR_POLICY_DOCUMENT_BASE64_ENCODED"/>
<input type="hidden" id="signature" name="X-Amz-Signature" value="YOUR_CALCULATED_SIGNATURE"/>
<input name="file" id="file" type="file"/>
<input id="btn_submit" class="btn btn-warning" type="submit" value="Upload File to S3">
</form>