Deploy an Agora RTC token server and join a video channel with token authentication

Verified steps

1. In Agora Console, create a project and enable App Certificate to require token authentication; download or clone Agora's open-source token server reference implementation (AgoraDynamicKey on GitHub) in your preferred language.
2. On your server, implement a token generation endpoint that accepts appId, appCertificate, channelName, and uid; use the RtcTokenBuilder from the SDK to call buildTokenWithUid() with a privilege expiry time in seconds (maximum 24 hours per token).
3. Return the generated token to your client; the client calls agoraEngine.joinChannel(token, channelName, uid, options) — uid and channelName must exactly match the values used to generate the token.
4. Handle token expiration on the client by listening for the onTokenPrivilegeWillExpire callback (fires 30 seconds before expiry); fetch a fresh token from your server and call agoraEngine.renewToken(newToken) without leaving the channel.
5. If the token expires before renewal, the SDK fires onConnectionStateChanged with the reason TOKEN_EXPIRED; the client must leave and rejoin with a new token.
6. For security, never embed your App Certificate in client-side code; always generate tokens server-side and invalidate compromised tokens by rotating the App Certificate in Agora Console (this invalidates all existing tokens).