Question:
I have multiple subdomains that I use on my site (sub1.my-domain.com, sub2.my-domain.com, sub3.my-domain.com, etc.). If I buy an SSL certificate will it work for all my subdomains?
Answer:
A regular certificate work for all domains, however it will give a warning on anything other than the domain it is issued to. The site will still be encrypted but the user’s web browser will get a warning about the name mismatch.
You can buy wildcard certs but they are pretty expensive.
If you just want encryption, a regular single-domain cert will work fine for all your subdomains. But if you need it to look correct on all domains (ie. no site-name mismatch warning from the browser) you’ll need either a wildcard cert or multiple single domain certs.