Question

Ok, I’m new to web development, so I might be getting some of these terms wrong. I apologize in advance.

I am having trouble understanding the different elements of authentication. Every method seems to be advised against by someone, though not always with clear reasons. I am building a web app for a company that will have access to a database, so I would like to make sure it is secure.

So the there are three places I have seen commonly used to store information.

1. FormsAuthentication.SetAuthCookie(). This stores a session cookie that will exprire with the browser, and nothing sensitive is on the client. However, it can only store one value. This stackoverflow answer shows a method of storing multiple values here, but the guy who gives it says not to use it, though not why.

2. FormsAuthenticationTicket. I don’t know where this information is stored, but it allows for a simple method of storing multiple values. Securing it, according to the documentation requires calling Encrpty() to store, and decrypt() to retrieve. This seems wasteful, but what do I know.

3. Session[“SomeRef”] = new CustomObject(). The second answer in this question explains how to do this, but a comment to it calls it dangerous because it can be stolen. This looks like the best method to me, because the information is still stored on the server, and can store multiple values.

I cannot find any comparisons for these methods, or good explanations on the “best practice” way of storing multiple pieces of information after authenticating a user. The information is just the User’s name and their userId.

Answer 1

Here is some further clarification to help you decide.

1. SetAuthCookie can be implemented in a way to store multiple values. In practice, however, you usually can’t store enough to avoid a database lookup. It’s best to store the user name (unique identifier) and load more information during the request. As your question suggests, you shouldn’t store sensitive information on it. You should assume that all information sent in a cookie can be decrypted and read and you should take precautions that that information can’t be used maliciously. All session cookies can be stolen and I’ll explain why in a moment.

2. FormsAuthenticationTicket is the same API as SetAuthCookie but at a lower level in the Framework. With SetAuthCookie, Encrypt() and Decrypt() should be happening anyway (it’s the default configuration.) It’s not wasteful but use method 1 instead because it’s easier.

3. Session has some limitations. Notably, by default it’s process-dependent. That means that when the server restarts or more than one web server is involved, your session is lost and you have to authenticate again. It is the easiest to use and fastest when using the default memory session storage (InProc). You can use sql storage or a dedicated session server to overcome the process-dependency.

All three methods are considered dangerous for the same reason all cookie-based authentication systems are dangerous: because the cookie’s value can be sniffed over wireless and reused to take over a session. This is known as sidejacking and it also applies to scenarios 1 and 2. The way to prevent this is to implement HTTPS. Then, the cookie transimission (and everything else) is encrypted at the network level and can’t be stolen.

TLDR; Use SetAuthCookie and HTTPS

NOTE this answer has been edited several times for clarity.