Some of our clients buy from us Certum certificates. To generate such a certificate, you need to provide a KID, an HMAC key, and an email address. Each domain has a different KID and HMAC key, but the email address remains the same.
This causes a problem because the authentication data is stored once, in a directory associated with the email address. As a result, to generate multiple Certum certificates on the same server - whether using lego or certbot - you need to use a separate configuration path for each certificate.
Please take this into account when implementing custom ACME SSL support.