I have site like
http://www.foo.comhttp://www.bar.comAnd I've a wildcard SSL cert *.example.com, instead of buying two SSL certs for the above two domains, can I re-use my existing wildcard SSL cert for wp-admin?
e.g.
http://foo.example.comhttp://bar.example.comOnly for wp-admin for better security, is it possible?
Yes, you can do this and it does not matter if plugins are different for the two sites, as you are not not using the same tables or anything.
Still, if you use plugins that are badly written and build resource urls on top the home url, these will have issues (404 errors mostly).
You don't say if is a multisite installation or two separate stand-alone ones.
I'm going to suppose it isn't multisite because if so, the answer is trivial. In the other case, there isn't any problem. You have to configure ssl as usual in your apache vhost or nginx for each domain with your wilcard certificate.
Aditionally, you can use the Wordpress HTTPS plugin to enable SSL only for wp-admin in each site (note that this plugin works in multisite also)
You'll have to use the HTTPS domain alias plugin, if you don't want to install multisite.
if they use the same plugins I see no problem.
you can use up even as symbolic link, getting simpler to maintain and update
Setting up MultiSite in one main domain, that you have SSL, and then use the other domain as custom sunrise domain settings. You have to setup the .htaccess or vhost(for NGiNX) though. But both site will need to have almost same type domain or plugin. Its one way.
Other will be a bit complex one. I would setup two separate WordPress in two separate subdomain. Then from the vhost file I will point other root domain also to that same sub domain's root folder. You will need some tweaking in vhost or .htaccess to dynamically rewriting domain, and also hardcode home and home directory url from wp-config.php. Its far more complex process, might need some trial and error testing.
BTW I hope you know you could even buy a SSL certificate as low at just $10 USD, and if you use service like CloudFlare, now even in their free package they provide free SSL support. Though its not actually true SSL, but might serve purpose for normal low-end need.
Try the beauty of multisite feature of wordpress. Here are some tutorial links:
So, guess your main site is http://example.com. Create two subsites:
As you have wildcard SSL so both subsites should be accessed with https://
Now, use a domain mapping plugin. WPMU DEV has a popular one. With that, you can map http://foo.example.com to http://foo.com and http://bar.example.com to http://bar.com
And you can access their admin by https://example.com/wp-admin or https://foo.example.com/wp-admin etc.
To enable the Network Setup menu item, you must first define multisite in the wp-config.php file.
Open up wp-config.php and add this line above where it says
/* That's all, stop editing! Happy blogging. */.
If it doesn't say that anywhere, then add the line somewhere above the first line that begins with require or include:
/* Multisite */
define( 'WP_ALLOW_MULTISITE', true );
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