That is just a link to the Server OS X download. I am running the server.
That said, when I checked my certificates it seems they do not expire until 26 Jan 2014. When I went to Key Chain access it is showing some older certificates. I deleted the old ones in accordance with what I found in this thread:
You probably have already figured this out but I thought I would post just in case anyone else has this same problem.
1. Open the server app.
2. Under the server group in the left hand column select your server.
3. Click on the Settings tab.
4. Click on the edit button across from "Enable Apple push notifications"
5. This will bring up a Apple Push Notifications window.
6. It should tell you when the certificate expires. Click the renew button on the right.
This should take care of the issue.
Hope this helps.
mac mini server (mid 2012), OSX 10.9, Server 3.0.1