Use C2PA tool with external signer using DigiCert's CSC APIs

C2PA tool is the official command-line utility from C2PA (Coalition for Content Provenance & Authenticity) that lets you inspect, create, sign and verify provenance manifests in media files. It supports the use of an external signer, whose role is to accept claim bytes from C2PA tool, produce the corresponding signature, and return it for embedding in the media file.  

This document explains how to use C2PA tool with an external signer and provides ready-to-use Rust sample code for building the executable signer that performs the signing using DigiCert’s CSC APIs.