System.DirectoryServices - The server is not operational

Question

I get an error by a website, on which I use Windows Authentication.

Strange things:

• Only occurs if user is not yet saved into database (new unknown user)
• Appears only on live system, everything fine on local development environment

This is what I get in a logging mail:

Source : System.DirectoryServices

Message: The server is not operational.

Trace:
at System.DirectoryServices.DirectoryEntry.Bind(Boolean throwIfFail)
at System.DirectoryServices.DirectoryEntry.Bind()
at System.DirectoryServices.DirectoryEntry.get_AdsObject()
at System.DirectoryServices.DirectorySearcher.FindAll(Boolean findMoreThanOne)
at System.DirectoryServices.DirectorySearcher.FindOne()
at Smarthouse.Labs.DataAccess.UserListManager.SaveUser(String windowsUserName)

This is how I implement DirectorySearch:

private void SaveUser(string windowsUserName)
{
    string[] domainAndUser = windowsUserName.Split('\\');
    string domain = domainAndUser[0];
    string username = domainAndUser[1];

    DirectoryEntry entry = new DirectoryEntry("LDAP://" + domain);
    DirectorySearcher search = new DirectorySearcher(entry);

    try
    {
        // Bind to the native AdsObject to force authentication.
        search.Filter = "(SAMAccountName=" + username + ")";
        search.PropertiesToLoad.Add("cn");
        search.PropertiesToLoad.Add("sn");
        search.PropertiesToLoad.Add("givenName");
        search.PropertiesToLoad.Add("mail");

        SearchResult result = search.FindOne();

        if (result == null)
        {
            throw new Exception("No results found in Windows authentication.");
        }

        User userToSave = new User();
        userToSave.FirstName = (String) result.Properties["givenName"][0];
        userToSave.LastName = (String) result.Properties["sn"][0];
        userToSave.Email = (String) result.Properties["mail"][0];
        userToSave.Username = windowsUserName;
        userToSave.Guid = Guid.NewGuid();

        SaveUser(userToSave);
    }
    catch (Exception ex)
    {
        throw new Exception("Error authenticating user. " + ex.Message, ex);
    }
    finally
    {
        //Dispose service and search to prevent leek in memory
        entry.Dispose();
        search.Dispose();
    }
}

If more code examples are needed just tell me.

Answer 1

Your problem is that you're using a "plain" domain name to bind - this won't work in LDAP. Actually, if you try to bind to LDAP://MyDomain, what you're really doing is trying to bind to the server called MyDomain.

You need a valid LDAP bind string - something like LDAP://dc=yourdomain,dc=local or something.

To find out what your default LDAP binding context is, use this code snippet:

DirectoryEntry deRoot = new DirectoryEntry("LDAP://RootDSE");

if (deRoot != null)
{
   string defaultNamingContext = deRoot.Properties["defaultNamingContext"].Value.ToString();
}

Once you have that string - use that as your bind string to your LDAP server.

And if you're on .NET 3.5 and up, you should check out the System.DirectoryServices.AccountManagement (S.DS.AM) namespace. Read all about it here:

• Managing Directory Security Principals in the .NET Framework 3.5
• MSDN docs on System.DirectoryServices.AccountManagement

Basically, you can define a domain context and easily find users and/or groups in AD:

// set up domain context -- no domain name needed, uses default domain 
PrincipalContext ctx = new PrincipalContext(ContextType.Domain);

// find a user
UserPrincipal user = UserPrincipal.FindByIdentity(ctx, username);

if(user != null)
{
   // do something here....     
}

The new S.DS.AM makes it really easy to play around with users and groups in AD!

Answer 2

You can use bind strings in the format LDAP://mydomain.com:389. I kept getting "Access is Denied" when trying to use the format LDAP://DC=mydomain,DC=com. Once I switched to the LDAP://mydomain.com:389 format, and bound using the AuthenticationTypes.ServerBind flag when constructing my DirectoryEntry, it worked great. This was in Azure App Service.

Answer 3

To add to marc_s's answer above, I needed to search multiple domains. So for each Domain I did the following:

DirectoryEntry deRoot = new DirectoryEntry("LDAP://" +"DomainName"+ "/RootDSE");
string defaultNamingContext = "LDAP://" + deRoot.Properties["defaultNamingContext"].Value.ToString();
DirectoryEntry mySearchRoot = new DirectoryEntry(defaultNamingContext);
DirectorySearcher myDirectorySearcher = new DirectorySearcher(mySearchRoot);