Daniel Hoelbling-Inzko talks about programming

Custom ASP.NET Membership provider

Posted by Daniel Hölbling on July 8, 2008

I've been ranting too much lately, so I guess it's time to get back into coding.

This time around I've been challenged with a new project that involves a legacy database, while my task is to rewrite the ASP.NET application that runs ontop of that database without actually touching the database.

So first: What is ASP.NET Membership?

Simple answer: A great way to build authentication with little to zero coding effort with very cool draggy-droppy developer experience :). You simply drag a Login control to your ASP.NET page and your application just learned how to authenticate and keep the session of users.

To achieve this on a already existing database you simply need to do one thing:

Implement the abstract class MembershipProvider and implement just one method: ValidateUser

public override bool ValidateUser(string username, string password)
    if (username == "tigraine" && password == "tigraine")
        return true;
    return false;
You see where I'm going here, you basically just need to return true or false given a username and a password. How you do it is entirely up to you as long as you return either true or false.

To make the magic actually work you need to add the new MembershipProvider (i've called it DBMembershipProvider) to your root web.config:

<authentication mode="Forms">
	<forms loginUrl="Login.aspx"></forms>
<membership defaultProvider="DBMembershipProvider">
		<add name="DBMembershipProvider" type="DBMembershipProvider" />
The <authentication mode="Forms"> is quite important because it tells asp.net to actually use forms driven authentication instead of windows authentication or microsoft passport. I also defined the loginUrl attribute to tell the app where to redirect anonymous users, but that's optional.

The membership stuff now is important, because here we glue the new provider into our system.

We just add a new provider in the <providers> section and name it conveniently, and most important: we tell .net what type to instantiate.

The defaultProvider property then tells .net what provider to use (if you've got multiple providers to log into your website, eg: Windows and Forms auth)

And, that's it. As long as the ValidateUser method returns true/false, your users can now use a fancy Login form to authenticate and their login session will get stored in a cookie. You can now drag LoginStatus and LoginName controls to your form and watch the goodness work :).

Hey! How do you actually secure something with this?

Yeah, I was so happy with that login working so I almost forgot to do this part. Usually you want to protect some files or directories from unregistered users. This also happens at the web.config level and is quite easy.

In case of a folder, just put a blank web.config in there and add the following directives:

		<deny users="?"/>
Now only registered users have access to this directory and you're done.

If you don't want to lock the whole directory but only some files in there you can do this through the verb attribute by either specifying a regex or a filename to be affected by your rule. (You could also use the <allow> tag to add exceptions to your deny tag I think)

Actually, if you look at the MembershipProvider, there's a ton more functionality I just skipped here. But this has been everything I needed to get login and user restriction for my current project, so I thought it's worth sharing how darn easy this actually is. If you want to delve deeper into the topic I'd suggest you either read 4GuyFromRolla or search through MSDN.

Filed under net, programmierung
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