If you have an active license directly with WHMCS (with active support if owned), this is already offered here. You must have a minimum of 5 branded (or unbranded) to start and must maintain this amount of licenses (or more). You may only sell licenses to your own hosting/dedicated customers.

One thing to note is that if you signup - an email will arrive with a contract to be signed. This step get's missed quite often and is a worthy mention.