x509 certs and XMPP servers

Ok, one last XMPP post for tonight.

I came across an interesting issue with our test XMPP server today. When the server was initially created, it was setup with an x509/SSL certificate that was self signed. That cert expired the other day, and I had to replace it.

Some of the people who were using the server started getting cert warnings while others did not. After a bit of investigating, I found the problem.

There are two ways that an XMPP client can connect to a server.

The first method is simple. You configure your client with your Jabber ID (username@company.com), and define an XMPP server (servername.company.com) to connect to. This is how our early documentation recommeded configuring your clients, but it is not the generally recommended method.

The second method is the preferred one. You define a service record (SRV record) in DNS for _xmpp-client._tcp.company.com which points to your server name. Once your client has your Jabber ID (JID), the client will automatically look up the SRV record, and connect to that service.

Now comes the cert warning. Apparently if you use an SRV record, your x509 cert needs to have a common name (CN) of company.com. If you define a server manually however, your CN needs to be the name of the server.

Our self-signed cert was for company.com. I replaced it by a properly signed cert for servername.company.com, and broke everyone using the preferred configuration method. Seeing the issue, I replaced it with a properly signed cert for company.com, and broke the people following the published documentation.

*sigh*

So now I get to update the documentation and answer the various questions for people. Longer term I'm going to see if its possible to provide certs for both methods. While you can't have two certs on the same port, it may be possible to either use a cert with an altCN, or possible have the SRV port point to a non-standard port so that people who define the server name can connect to the default port number (5222/5223).