Is your feature request related to a problem? Please describe.

It would be good if you could specify the duration of time you would like the login token to be valid for. For our use at least, the result of .createCustomToken is mostly used immediately after being provided to the client, so we'd like to have a very short expiry time.

Describe the solution you'd like

Update .createCustomToken or a new method .createCustomTokenWithOptions that takes an expiry.

Describe alternatives you've considered

Using the details from create custom tokens using a third-party JWT library, but this seems a bit redundant when the SDK is so close to providing what is needed.