For optional use before
join(). Does a pre-authentication with the server. Returns a Promise that resolves with the user's current access state.
Pre-authenticating unlocks some pre-
join() info that would only otherwise be available post-
join(), such as:
preAuth() takes the same call properties argument as the factory methods or
join(). At a minimum, the following must be provided:
token are "locked in" upon invoking
preAuth(), and cannot be changed on
join() (any attempt to do so will result in an error).
If the call machine bundle isn't already loaded, it will be loaded.
Pre-authenticating will give access to the local participant through a
"participant-updated" event. To start the local participant's camera in the pre-authenticating stage (before joining the call), use with