Permissions offer APIs for viewing and managing permissions. In release 8.5, permissions is an extensibility point.
In-process API permissions methods: Permissions In-Process API Service
REST API permissions endpoints: Permission REST Endpoints
Because permissions are assigned to roles, also review the In-process and REST APIs for viewing and managing roles including adding a user to a role, removing a user from a role, etc.
Alex Crome created a permission viewer application that is both useful as a diagnostics tool and as a good reference example for working with the Zimbra Social REST roles and permissions endpoints.
Find Alex's Telligent Evolution Permission Viewer on GitHub.
The permission viewer application is a diagnostic tool for viewing permissions in the Zimbra Social platform. It allows you to view permissions in a tabular form which can make diagnosing permission based issues easier.
It uses the Zimbra Social platform REST API to pull data out of a Zimbra Social platform community.