Net::Amazon::S3::Policy gives you an object-oriented interface to manage policies for Amazon S3 HTTP POST uploads.

Amazon S3 relies upon either a REST interface (see Net::Amazon::S3) or a SOAP one; as an added service, it is possible to give access to the upload of resources using HTTP POSTs that do not involve using any of these two interfaces, but a single HTML FORM. The rules you have to follow are explained in the Amazon S3 Developer Guide.

More or less, it boils down to the following:

• if the target bucket is not writeable by the anonymous group, you'll need to set an access policy;
• almost every field in the HTML FORM that will be used to build up the HTTP POST message by the browser needs to be included into a policy, and the policy has to be sent along within the HTTP POST
• together with the policy, also the bucket owner's AWS ID (the public one) has to be sent, together with a digital signature of the policy that has to be created using the bucket owner's AWS secret key.

This module lets you manage the build-up of a policy document, providing you with tools to get the Base64 encoding of the resulting JSON policy document, and to calculate the Base64 encoding of the signature. See "Example" for a complete example of how to do this.

In addition to policy synthesis, the module is also capable of parsing some policy (base64-encoded or not, but in JSON format). This shouldn't be a need in general... possibly for debug reasons.