Friday, May 17, 2013

Updating Web-login for Javascript Webapp

I've been coding away for several days on some old web-login logic I had implemented in littleware to work in web applications with JSF-managed UX. I'm updating the code for use in apps where a javascript program manages the user experience. I've been thinking lately about the similarities and differences between the two application architectures.

The first difference between the two designs is in deployment. The old JSF architecture relied on JSF and JSP templates managed by the server, so I would usually bundle up the entire application in a .war file, and deploy it to some glassfish or tomcat or whatever container. The user interacted with the application by clicking links and submitting forms that moved the browser between web pages rendered by the server.

I'm trying to structure the newer code so that most client-side assets (javascript, CSS, hadlebar templates, ...) are served as static files from S3. The user's in-browser interactions with the application trigger events that are handled by javascript event-handlers. The javascript code running in the user's browser can access remote services via cross-origin AJAX requests. There are various CORS servlet filters open sourced online that take care of setting the HTTP response headers that browsers look for; today I grabbed this one posted by some Ebay coders to github - hopefully it works.

In the login code, both the old and new setups rely on a request filter (javax.servlet.Filter) to intercept unauthenticated client requests. The old code would intercept an unauthenticated page-load request, and forward the request on the server to a login page via RequestDispatcher.forward.

The new code intercepts unauthenticated AJAX requests to JSON services, and responds to the javascript client with an HTTP 401 (unauthorized) response, and relies upon the javascript code on the client to initiate a login process that eventually authenticates with the server by submitting credentials to a login AJAX service.

Finally - in the older applications I had the bad habit of tracking session state on the server via beans stashed in container-managed in-memory session. Tracking user data in-memory on a particular server required that a client continued to interact with the same server it began a session with. In-memory session state also made it difficult to partition a server's functionality between different endpoints. In other words - if I had a server that implemented some functionality "ABC", and I later decided that I would like to split the functionality on that server (or server cluster) between separate "A", "B", and "C" servers (or clusters), then it would be hard to do that if the code relied on shared in-memory session state.

Anyway, the new code avoids session state on the server - instead it relies on the client-side javascript code to track session state in most cases, and transient cookies in a few others.

In the end - I get to throw away a bunch of crazy server-side JSF beans and templates, and replace them with javascript modules and REST services.

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