I'll make a guess, but it is just a guess. The user wants to use the client authentication feature of SSL to authenticate to a website, instead of username/password. SSL's client authentication is certificate-based.
I would think googling on something like "tomcat ssl client authentication" would get you information on how to configure tomcat to do this.
Nice to meet you.
Forget this weirdo. You guys wanna see something really neat? I just have to take off my shoe .... (hint: it's a tiny ad)