That particular feature is still on the wishlist, but you can already restrict new affiliate sign-ups to those you have vetted and approved. In Seller Admin > Edit Affiliate Program Settings, un-check "List affiliate program in E-junkie Marketplace", and also remove any sign-up links you have posted on your site or elsewhere, and optionally replace them with a link to your site's contact form with suitable link text (e.g., "Click here to apply for our affiliate program").
This way, new affiliates will need to apply to join by contacting you, then if you approve, you can personally email them your sign-up link URL, which would be the href= URL from your sign-up code, like this example (the XXX and YYY parts would of course be unique to your own link):
https://www.e-junkie.com/affiliates/?cl=XXXXXX&ev=YYYYYYYYYY