Who said it must be done during training? Most of the enterprise data is accessed after training - RAG or MCP tool calls. I can see how the techniques I mentioned above could be applied during RAG (in vector stores adopting Apache Accumulo ideas) or in MCP servers (MCP OAuth + RFC 8693 OAuth 2.0 Token Exchange + Zanzibar/Biscuit for faithfully replicating the authz constraints of systems where the data is being retrieved from).