Get a list of all channels that a given user have access

How an app can retrieve the list of channels that the user has access to?
A query to host:4984/DB/_session yields:

    "authentication_handlers": [
    "ok": true, 
    "userCtx": {
        "channels": {
            "!": 1, 
            "ADMIN_CHANNEL": 5, 
            "public": 2
        "name": "USER"

In this case the channels property doesn’t contains all the channels that are assigned by the sync_function, channels computed from roles aren’t listed.
Should I write a wrapper for host:4985/DB/_user/USER and read the all_channels result?

In some use cases the set of channels could be considered sensitive data that the admins don’t want the user to see, so we don’t provide access to it except on the admin port.