In your proxy.conf file:

# Blackhole (REJECT) where the realm is missing.

realm NULL {
}

# Realms that don't match any other listed send to the pool of govroam servers
realm "~^[^@.]([a-zA-Z0-9-]+\.)+[a-zA-Z]{2,6}$" {
    auth_pool = govroam
    nostrip
}