Working with DirectoryServices in ASP.NET Core

If you only want to authenticate users in .NET Core 2.0, you only need to add System.DirectoryServices Nuget package (no need to add Microsoft.Windows.Compatibility nuget package). It is also supported in .NET Standard 2.0

Note: I've only used below code in .NET Core 2.2, but the nuget compatibility info indicates that it works in .NET Core 2.0.

To validate password use:

var domainAndUsername = domain + @"\" + username;
var entry = new DirectoryEntry(_path, domainAndUsername, pwd);

object isValidPassword = null;
try
{
     // authenticate (check password)
     isValidPassword = entry.NativeObject;
}
catch (Exception ex)
{
      _logger.Log.Debug($"LDAP Authentication Failed for {domainAndUsername}"); 
      return false;
}

Furthermore, if you want to search for user in directory, below should work:

var search = new DirectorySearcher(entry) { Filter = "(SAMAccountName=" + username + ")" };
search.PropertiesToLoad.Add("cn");

var result = search.FindOne();

According to Github Issue, System.DirectoryServices.AccountManagement isn't yet supported for LDAP. Beyond that, previous info provided by @zdub and @Bastyon still seems valid.

Adding to Bastyons answer above, you can install System.DirectoryServices.AccountManagement in a .NET Core app as a NuGet package (preview version) from https://www.nuget.org/packages/System.DirectoryServices.AccountManagement/4.5.0-preview1-25914-04. Once installed, you can create a simple call to authenticate an AD user as follows:

public static bool ValidateCredentials(string userName, string password)
{
    try 
    {
        using (var adContext = new PrincipalContext(ContextType.Domain, "YOUR_AD_DOMAIN"))
        {
            return adContext.ValidateCredentials(userName, password);
        }
    }
    catch(Exception ex) 
    {
        throw ex;
    }
}

Update: This package is now available as a final version from https://www.nuget.org/packages/System.DirectoryServices.AccountManagement

Just want to say that they just issued a pre-release of the Microsoft.Windows.Compatibility which contains the System.DirectoryServices components needed to work directory with active directory. its beta, but its finally out there.

• NuGet Microsoft.Windows.Compatibility

The new CoreCLR doesn't support this library, at the moment. There's an open GitHub issue about this, where you can find more information and discussion. (A workaround is presented there if you are only using AD for your authentication system.)

If you're only planning on running this app on a Windows server, you could target "net452" for the framework and add the framework assemblies underneath that.

"frameworks": {
  "net452": {
    "frameworkAssemblies": {
      "System.DirectoryServices": "4.0.0.0",
      "System.DirectoryServices.AccountManagement": "4.0.0.0"
    }
  }
},