S3-Uploader
Jonathan Wight’s S3-Uploader project shows how to upload to Amazon S3 directly without exposing an AWS_SECRET_ACCESS_KEY to your clients:
Sample Python and Objective-C showing how to upload to Amazon S3 without uploading through an intermediate web-service. The basic theory is explained here.
Project consists of a sample Python Flask based server app (suitable for hosting on heroku) that hosts a simple upload form that uploads files directly to Amazon S3.