This program can be configured as an external signing command in poudriere.conf
to sign package repositories using a key stored in Azure Key Vault.
It takes one parameter: the key URI to be used for signing. Credentials can be passed
in via the AZURE_CLIENT_ID, AZURE_CLIENT_SECRET, and AZURE_TENANT_ID variables; but
unless it's for testing you'll want to use a managed service identity, which is used
by default as long as there's only one (system- or user-managed) available.
This is not an official Microsoft project.
