Classroom RTC Token Design: Room Identity, Permissions, and Client Trust
The article discusses the design of an RTC room token, which carries identity and permissions across an untrusted client before it reaches a realtime service. The token should contain a server-asserted subject, a narrow room audience, explicit capabilities, and a short validity window. It should not carry authority merely because the browser supplied a user name or room ID.
The article emphasizes the importance of authenticating the student or instructor on the application backend, authorizing the requested class session there, and minting a narrowly scoped credential. The realtime edge verifies the token and derives connection state from verified claims. The article also highlights the need for a signed JSON Web Token with registered claims such as sub for the subject, aud for the intended audience, exp for expiration, nbf for the time before which it must not be accepted, and jti for a token identifier.
The article stresses that the authorization service must assign classroom semantics and reject an audience mismatch, rather than treating aud as descriptive metadata.
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