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The Lowdown on ASP.NET Authentication

  • By Karl Moore
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Forms Authentication, Without Web.config

The sort of Forms authentication discussed above is, however, relatively limited. Unless you have just a few core user groups, which can be easily stored in Web.config, it's not awfully useful. And the passwords are stored in plain text XML, which means that anyone in your development team could retrieve them (unless you encrypt to MD5 format and change the passwordFormat attribute).

So, how can you authenticate users using information from a database, say?

It's easy: simply omit the .Authentication method in the procedure. In its place, add your own code, perhaps querying a table using ADO.NET code and validate the provided information. If it's acceptable, run the .RedirectFromLoginPage method. Everything else will work as normal.

Note that, if you want to remove the sample users from your Web.config file, you need to replace the whole <authentication><form>...</authentication> section with just <authentication mode="Forms" />.

Authenticating Just Part of Your Site

Sometimes, you don't want to authenticate all of your Web application. In some situations, you may just want to keep a couple of pages, such as a basket checkout form, available to only those authorized users.

Yes, you could try doing it manually by remembering some sort of session variable and/or by using cookies. But a much neater solution is to use a little-known trick that allows you to still use ASP.NET Forms authentication, but only with an exclusive number of pages on your site.

Here's how:

  1. Alter your Web.config file so that it uses Forms authentication. You can do this by following the first step in the "Five Steps to ASP.NET Authentication" tip, if you'll be using Web.config to store the users. Or, simply change the <authentication> element to <authentication mode="Forms" /> if you're going to authenticate using your own database, et cetera. In this tip, however, we're not going to deny regular, unauthenticated visitors.
  2. Still in your Web.config file, just underneath the <configuration> element, add the following code, replacing "checkout.aspx" with the page you want to protect. This will ensure that ASP.NET denies access to any unauthenticated users attempting to view this page. You can add as many <location> blocks as you wish and can include filenames and folders in the path.
  3. <location path="checkout.aspx">
            <deny users="?" />
  4. Go ahead and create your login.aspx page as you did in the last tip.

And that's it! You've created a Web application that uses Forms authentication but grants access to all users by default. You've then added a clause in Web.config that states all those users who are attempting to view checkout.aspx must be authorized first—and are therefore redirected to login.aspx when they access the page.

Note that these changes to the Web.config file are the only real difference to the authentication process. The other methods of logging out, retrieving the username, and so on all work in exactly the same way as with full authentication.

About the Author

Karl Moore (MCSD, MVP) is an experience author living in Yorkshire, England. He is author of numerous technology books, including the new Ultimate VB .NET and ASP.NET Code Book, plus regularly features at industry conferences and on BBC radio. Moore also runs his own creative consultancy, White Cliff Computing Ltd. Visit his official Web site at www.karlmoore.com.

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This article was originally published on January 14, 2004

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