I've got three different apps, all in GWT, none using Spring. Today, all of them got their own security layer provided by Tomcat. I want to setup a security layer shared by all of them. So that I don't have to deal with changes in the security layer for every app (following the DRY principle). I believe it's something similar to what Google does. Every time I try to login to any Google app, I'm taken to account.google.com.
How can I do that? Maybe setting this webapp Accounts to deal with every aspect of the accounts (log in and out, edit account, etc), and connect the session (or authentication) to my webapps?
You could deploy a Central Authentication Service and use it as an authentication provider for your applications.
Using a library (for example gwt-cas) to call your CAS will reduce your code duplication to a few lines of configuration per project.