It's tough to find the time to read a book cover to cover. In fact, it's been a while since I've read a book from beginning to end. Typically I'm only interested in a few chapters which I then read. Later, when the need arises, I may get back to other chapter. It's like treating a book like an encyclopedia or a dictionary. I bet that most people read technical books that way nowadays. So it's important that a book lends itself to be read that way.
Security is a very broad field with many many different topics, e.g. user authentication and authorization in web applications, integration with an external security server, web services security, and so on. Fortunately, very few people will have to deal with all these aspects at the same time. GlassFish Security covers many if not all of those aspects, and that's another reason why it should be possible to read this book like an encyclopedia.
I went back in time and tried to remember all the times that I have had anything to do with security in GlassFish and checked what the book had to say about it. For instance, to start simple, there's the issue of configuring realms and users. There's the time I tried to get JSPWiki to work on GlassFish using declarative authentication and authorization, something that goes through server.policy. More advanced, there's the time we tried to integrate GlassFish with AccessManager. On all these topics, the book delivers. There are many other topics (e.g. integration with OpenSSO, securing JMX, etc), all described in detail without wasting much space on repetition or endless code or XML listings. The book would have saved me a lot of time had I had it at the time when I needed it.
If you're using GlassFish, this book belongs on your bookshelf!