How to authenticate LDAP user with GSS negotiate binding authentication using C#?

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C#

Binding

LDAP

authentication

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I am new to LDAP. I have written the below code that authenticates users with LDAP. I currently have to validate users with a server that has a biding authentication type of GSS-Negotiate. I couldn't find any examples to validate the user with such a binding authentication type. The below code I tried doesn't work on this binding authentication. What am I missing in the below code segment. Any help would be much appreciated. Also is there an internet LDAP server in which I can validate a user with GSS-Negotiate binding to test it out?

What I have tried:

<pre lang="c#">

<pre>public static string AuthFunction_One(string identity, string password, string containerString, string adServerName, bool useLDAPS, IdentityType identityType)
    {

        string failedString = "FAILED";
        string successString = "SUCCESS";
        string returnValue = failedString;

        try
        {
            PrincipalContext ctx = null;
            if (useLDAPS)
            {
                ctx = new PrincipalContext(ContextType.Domain, adServerName, containerString, ContextOptions.Negotiate | ContextOptions.SecureSocketLayer);
            }
            else
            {
                ctx = new PrincipalContext(ContextType.Domain, adServerName, containerString);
            }
            UserPrincipal oUserPrincipal = UserPrincipal.FindByIdentity(ctx, identityType, identity);
            PrincipalSearchResult<Principal> oPrincipalSearchResult = oUserPrincipal.GetGroups();
            try
            {
                foreach (Principal result in oPrincipalSearchResult)
                {

                }

            }
            catch (Exception ex)
            {
                NLogHelper.GetInstance().Log("ADUtilityClass", "AuthFunction_One", NLog.LogLevel.Debug, "Failed to probe groups. Ex: " + ex.ToString());
            }

            if (ctx.ValidateCredentials(identity, password))
            {
                return successString;
            }
            else
            {
                return failedString;
            }
        }
        catch (Exception ex)
        { 
            NLogHelper.GetInstance().Log("ADUtilityClass", "AuthFunction_One", NLog.LogLevel.Debug, "Error in function. Ex: " + ex.ToString());
            return failedString;
        }
    }