How do you handle metadata filtering in RAG to implement access control?

Metadata filtering in RAG enables access control by tagging each document chunk with permission metadata during indexing. Tags include department, security classification, document owner, project, and role-based access levels. At query time, the user identity and role are resolved, and metadata filters are applied before or during vector search to restrict results to authorized documents only. Most vector databases support pre-filtering where metadata conditions are applied before similarity search, and post-filtering where similarity search runs first then results are filtered. Pre-filtering is preferred for access control to avoid retrieving and then discarding unauthorized content. The metadata schema should mirror your organization existing permission structure. This ensures the AI assistant never reveals information from documents the user does not have access to, which is critical for enterprise deployments with compartmentalized information.