Problem Description: 

User might need to sign individual collection, or to add additional signature or
To redo a broken signature on existing collection.

QA Criteria: 

• Ensure it is possible to sign a specific collection version via API
• Ensure it is possible to sign all the collection versions under specified namespace or repository via API

Proposed Solution: 

collections/sign/ -d "payload"

Signing a single collection version:

-d "signing_service:name, namespace:, collection:, version:"

Signing all version under a collection repo

-d "signing_service:name, namespace:, collection:"

Signing all versions of all collections under a namespace

-d "signing_service:name, namespace:"

Reminder: API