Interacta is a live audience-engagement platform split into seven Spring Boot services and a Python worker, talking over Kafka rather than HTTP. A host creates a session, puts a join code on screen, and the room participates in real time — questions, upvotes, live polls and shared handouts — while STOMP over WebSocket fans every change out to the connected clients.

The defining constraint is that listeners never create an account. Joining a session mints a signed, PII-free participant token, so an anonymous listener is still a first-class API caller and one upvote per person is still enforceable. Every service validates two token issuers — Keycloak for staff, session-service for participants — and asks the same question of both: is this caller the host of this session, or a participant scoped to it?

The API, not the UI, is the security boundary: a hidden poll tally is zeroed in the DTO rather than merely unrendered, realtime frames are deliberately thin so the server decides what each viewer may see, and every service verifies its own tokens instead of trusting one check at the gateway. A Python AI worker screens questions for toxicity and clusters near-duplicates before they ever reach the room.