I have a web app, and when users sign up, we give them their own subdomain, e,g, user1.website.example
We do this with a wildcard ssl for *.website.example
However, users are requesting custom domains.
So we plan on letting them point a CNAME to our system.
So when the user creates a CNAME "register.user1website.example" points to "user1.website.example", we pull that CNAME from the db and server the correct content - all works hunky dory...
BUT How do we allow the users domain to have a SSL?
Our system auto redirects from http to https, so they would get an insecure warning. Obviously, for the moment we have stopped the redirect, but we want everyone to have a SSL.
We're also talking about 10k+ users, so I don't want to have to have the domain added into Plesk and Lets Encrypt, as it changes all the time, and it would be a nightmare for management.
I especially don't want to have to manually add domains and SSLs in our plesk panel whenever someone wants to add a custom domain.
I have looked into SAN SSLs, but they only allow up to 100 domains - is there another method I can use that will serve me better?