We have bought an SSL certificate for https://www.domain.com.
Users will be accessing the domain at https://sub1.domain.com, https://sub2.domain.com, etc.
I would like to be able to redirect those subdomains, via Apache. So for instance, https://sub1.domain.com becomes https://www.domain.com/sub1.
Is this possible to do without presenting the user with a "Insecure Connection" error?
If you purchased a wildcard certificate for *.domain.com or had sub1.domain.com and sub2.domain.com listed as Subject Alternative Names on the certificate, you'll be fine. If you bought the cert just for domain.com, then you're out of luck. The users will always see it, since the cert is not valid for that sub-domain and is only valid for domain.com/*.
No, because the SSL connection is setup before apache receives the hostname the connection is made with.
You can use startssl.com to obtain certificates for free. At least:
This is not really of help though, because you can't put multiple certificates on the same IP. You could only do this with a multi domain certificate or a wildcard certificate (but wildcard certificates have their limitations).