SSL issues for authentication (web and webdav)

Hi

I would like to secure the access for content edition to a Jahia 
deployment handling 2 virtual sites with different domain names 
(www.domain.com and www.subsite.domain.com)

1) Can I have a single certificate for https://securelogin.domain.com 
for both virtual sites ? Or a specific certificate is required for each 
site ?

2) Is it enougth to change the protocol of the login page URL, or any 
specific settings should done to preserve sessions between the 2 protocols ?

3) Jahia 4.0.4 is bundled with Jakarta Slide 10.0.16 (as far as I can 
find out). Is it possible to have authentication through SSL for this 
version ?
Is there any best practice to restrict the authentication to given IPs 
without disabling the read only access of visitors of the public web site ?

Thanks for your inputs

Regards

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