I am soon launching a SaaS static HTML web building service website. Currently when a user signs up they have an option to use a sub domain name of their choosing based off of my main domain and will be SSL enabled because my site is. (I think)
They do have an option to use their own domain but they would currently have to supply their own SSL certificate. As I understand it one of the only ways for them to receive a certificate would be through some sort of hosting service. They would be able to sync my web builder to their host through FTP no problem if they want to do it that way.
However they have an option to just forward their domain to my site which would do the hosting for them, so I’m curious how a SSL could be supplied to them by just forwarding to their custom sub domain on my site.
I know with Wix web builder a while back you would have to purchase a domain through them in order to get an SSL, but I believe they can supply their users with a certificate now even if they didn’t purchase through them.
So I’m curious how I would be able to supply SSL certificates to users in the same manner who choose to host their own domains on my site.
as you controls main domain, you would ve ablue to use wildcard cert as fallback.
but if you didn’t registed your domain as public suffix a subdomain per client will hit rate limit quite fast (as it’s just 50 cert/week.
Once someone points their domain at your web server, it's possible for you to get a certificate using HTTP or TLS-ALPN validation, just like anyone else.
(DNS validation would also be possible if you ask them to use CNAME or NS records to point the _acme-challenge.www.example.com subdomain to DNS servers under your control, but that's more work.)
If you're asking for specific software recommendations, I don't know. I believe many large scale integrations use quite customized software, since there weren't always many options available, and people had to integrate them into their existing management systems anyway. There are good options, but I don't want to specifically endorse something.