Add list of blacklisted domains

[Scorcerer]

Hello, it would be great if there was a possibility to declare a list of domains that won't be available to generate certificates for. The problem is: all accounts are created with the same main domain (as in: customer01.brandname.com, customer02.brandname.com, anothercustomer.brandname.com) which eventually triggers let's encrypt rate limit of 20 subdomains per week. With this list, customers wouldn't be able to try to create such certificates, and problem with LE rate-limiting shouldn't be an issue.

[crazybejbi]

It would be very important, becouse many hosting providers is seting up account with "technical domain" which is subdomain of his own domain. These subdomains have usually wildcard paid certyficate, so, don't need let's encrypt certyficate. When it will be "blacklist of domains" users (when generating let's encrypt) will not see subdomains contained such "blacklisted domains". Subdomains have limit up to 20 per week when generating.

[will-ashworth]

Not intending to troll this comment thread, but it's related...so here goes.

If the main reason for rate limiting is usage of the API (and expense to operate it), why not charge for use of the API like Google does? Seems pretty straightforward to me.