Generic Authentication Call to Active Directory in C#

Question

I would like to have a clean C# class that authenticates from Active Directory.

It should be pretty simple, it just has to ask for credentials and check if it matches what AD is expecting.

I am responsible for a number of C# applications, and I would like all of them to use the same class.

Could someone please provide a clean code sample of such a class? It should have good error handling, be well commented, and specifically ask for credentials rather than try to read if a user is already logged in to AD for another application. (This is a security requirement because some applications are used in areas with shared computers: People with multiple roles and different permission levels may use the same computer and forget to log out between sessions)

Answer 1

There's some reason you can't use Windows integrated authentication, and not bother users with entering their names and passwords? That's simultaneously the most usable and secure solution when possible.

Answer 2

http://support.microsoft.com/kb/316748

public bool IsAuthenticated(String domain, String username, String pwd)
{
  String domainAndUsername = domain + "\\" + username;
  DirectoryEntry entry = new DirectoryEntry(_path, domainAndUsername, pwd);

  try
  { //Bind to the native AdsObject to force authentication.   
     Object obj = entry.NativeObject;

     DirectorySearcher search = new DirectorySearcher(entry);

     search.Filter = "(SAMAccountName=" + username + ")";
     search.PropertiesToLoad.Add("cn");
     SearchResult result = search.FindOne();

     if(null == result)
     {
         return false;
     }

     //Update the new path to the user in the directory.
     _path = result.Path;
     _filterAttribute = (String)result.Properties["cn"][0];
  }
  catch (Exception ex)
  {
     throw new Exception("Error authenticating user. " + ex.Message);
  }

     return true;
 }

Answer 3

Admittedly I have no experience programming against AD, but the link below seems it might address your problem.

http://www.codeproject.com/KB/system/everythingInAD.aspx#35