Question: Azure provides shared access signatures ([[1](http://msdn.microsoft.com/en-us/library/windowsazure/ee395415.aspx)], [[2](http://msdn.microsoft.com/en-us/library/windowsazure/dn140255.aspx)], [[3](http://msdn.microsoft.com/en-us/library/windowsazure/dn140256.aspx)]) that can delegate access (read/write) to specific blobs/containers/tables/queues in an Azure Storage account using an access key generated through the REST API. Does AWS offer a similar feature?

Answer: 
It is almost identical to what Azure provides, just without a special name like SAS. See <http://docs.aws.amazon.com/AmazonS3/latest/dev/RESTAuthentication.html> for details.
I haven't tried it yet but looks like pre-signed URLs are the thing: See the "Amazon S3: Getting a pre-signed URL for a PUT operation with a specific payload" section of <http://docs.aws.amazon.com/AWSJavaScriptSDK/guide/node-examples.html>