[Question] What's the best way to know whether the user is Broadcaster or Viewer?

Nope.

You can parse/decode the JWT client side.

Split the JWT around . (periods).

The first part is the alogirthm, the second is the data (as a JSON object) and the third is the validator. If you don’t care about validation, you can parse/decode client side and read the data and skip validation. Course don’t do that for something where you need it to be valid, but saves me a lookup to see if the user has shared their ID.

Or just test the OpaqueID for being of the form of “broadcaster”