[Connector] Add authentication to WebRTC datachannel & validate match data DTOs

[Flegma]

Summary

WebRTC data channel handlers and match data endpoints need authentication and input validation.

Tasks

• Add authentication verification to WebRTC data channel message handlers
• Validate data before writing to shared storage
• Create proper DTO classes with NestJS validation pipe
• Add rate limiting to data channel messages

Impact

Could allow unauthorized data to be processed or stored.

Details

Full details in internal audit document. Finding IDs: CRIT-CONN-03, CRIT-CONN-04

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Related Issues (Input Validation Pattern)

• [API] Harden match events gateway authentication and message validation #371 — [API] Harden match events gateway validation
• [Connector] Sanitize user input in offline match manifest generation #404 — [Connector] Sanitize offline match manifest input
• [Connector] Add command validation and whitelist to RCON gateway #405 — [Connector] Add RCON command whitelist
• [Connector] Add authentication to WebRTC datachannel & validate match data DTOs #406 — [Connector] Validate WebRTC datachannel & match DTOs
• [Game Server] Async void anti-pattern & missing command input validation #402 — [Game Server] Missing command input validation