ASP.NET Core 2.0 LDAP Active Directory Authentication

I have found a lot of information from the past saying that LDAP authentication isn't enabled yet but you can get around that using third party packages. However, it seems that LDAP authentication WAS implemented back in January. I can't seem to find any information on HOW to implement it.

I already have custom authentication set up in my project, I just need the logic to fill in the HandleAuthenticateAsync method.

I have tried using other examples, but they don't seem to work with .NET Core 2.0.

Here is the only relevant code that I have that I can think of posting

protected override Task<AuthenticateResult> HandleAuthenticateAsync()
{
    // Get Authorization header value
    if (!Request.Headers.TryGetValue(HeaderNames.Authorization, out var authorization)) {
        return Task.FromResult(AuthenticateResult.Fail("Cannot read authorization header."));
    }

    // TODO: Authenticate user

    // Create authenticated user ticket
    var identities = new List<ClaimsIdentity> { new ClaimsIdentity("custom auth type") };
    var ticket = new AuthenticationTicket(new ClaimsPrincipal(identities), Options.Scheme);

    return Task.FromResult(AuthenticateResult.Success(ticket));

    // else User not authenticated
    return Task.FromResult(AuthenticateResult.Fail("Invalid auth key."));
}

So, my question is, how do I implement LDAP Authentication in .NET Core 2.0?

Thanks to Win's Answer for pointing out that I needed to use Windows Compatibility Pack, I was able to figure this out.

The first thing I had to do was install the Nuget package

Install-Package Microsoft.Windows.Compatibility 

At the time, I needed a preview version, so I appended -Version 2.0.0-preview1-26216-02 on the end of this command

Then, add using statements for System.DirectoryServices and System.DirectoryServices.AccountManagement

Then, just plug this logic into my HandleAuthenticateAsync method:

const string LDAP_PATH = "EX://exldap.example.com:5555";
const string LDAP_DOMAIN = "exldap.example.com:5555";

using (var context = new PrincipalContext(ContextType.Domain, LDAP_DOMAIN, "service_acct_user", "service_acct_pswd")) {
    if (context.ValidateCredentials(username, password)) {
        using (var de = new DirectoryEntry(LDAP_PATH))
        using (var ds = new DirectorySearcher(de)) {
            // other logic to verify user has correct permissions

            // User authenticated and authorized
            var identities = new List<ClaimsIdentity> { new ClaimsIdentity("custom auth type") };
            var ticket = new AuthenticationTicket(new ClaimsPrincipal(identities), Options.Scheme);
            return Task.FromResult(AuthenticateResult.Success(ticket));
        }
    }
}

// User not authenticated
return Task.FromResult(AuthenticateResult.Fail("Invalid auth key."));

According to #2089, it is only available in Windows Compatibility-Pack for .NET Core. I currently use Novell.Directory.Ldap.NETStandard.

public bool ValidateUser(string domainName, string username, string password)
{
   string userDn = $"{username}@{domainName}";
   try
   {
      using (var connection = new LdapConnection {SecureSocketLayer = false})
      {
         connection.Connect(domainName, LdapConnection.DEFAULT_PORT);
         connection.Bind(userDn, password);
         if (connection.Bound)
            return true;
      }
   }
   catch (LdapException ex)
   {
      // Log exception
   }
   return false;
}

For authentication and authorization, we can use Cookie Authentication Middleware with claims.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, 
   ILoggerFactory loggerFactory)
{
   app.UseCookieAuthentication(new CookieAuthenticationOptions
   {                
      AuthenticationScheme = "AuthenticationScheme",
      LoginPath = new PathString("/Account/Login"),
      AccessDeniedPath = new PathString("/Common/AccessDenied"),
      AutomaticAuthenticate = true,
      AutomaticChallenge = true
   });
}

It has few moving pieces, so I created a working sample project at GitHub. There are two main pieces - LdapAuthenticationService and SignInManager.

namespace: System.DirectoryServices.AccountManagement;



 public bool UserAuthentication(string username, string password)
 {
        PrincipalContext pc = new PrincipalContext(ContextType.Domain, "<DOMAIN NAME>");
        bool isValid = pc.ValidateCredentials(username, password);
        return isValid;
 }