There are only a few things you need to do, actually. It's mostly around:- Creating a realm (probably by extending AuthorizingRealm)
- Creating a filter (probably by extending AbstractShiroFilter). Alternatively, you can use their INI filter, which provides some DI-like things, if you're not using something like Guice.
I think Shiro is far easier to use than Spring Security, personally. However, the hard part is there is a lot more and better documentation for Spring Security. I also find Shiro to be relatively light-weight, like Guice, in comparison with Spring. I like Spring a lot, don't get me wrong, but there are reasons for it and Guice, depending on your needs.