Letter

Letter is a PostgreSQL extension implementing relationship-based access control (ReBAC). It enforces row-level and column-level read and write permissions based on relationships between rows, enabling dynamic, scoped access rights in databases. It supports scoped and global grants, membership rules, and integrates via triggers and planner hooks for transparent enforcement. It's designed for PostgreSQL 16 and 17 and intended for use by applications setting user identity at the session level.