Principle context return null value in asp.net mvc

I am trying to connect with active directory using principle context. i have tried with below code.

using (var context = new PrincipalContext(ContextType.Domain,
                        ConfigurationManager.AppSettings["DomainName"].ToString()))
                    {
                        try
                        {
                            writeLog("Before:" + isCheckUserName);
                            writeLog("Context name:" + context.Name);
                            var user = UserPrincipal.FindByIdentity(context, GetCurrentWindowsLogin());

                            writeLog("GetCurrent:" + GetCurrentWindowsLogin());
                            writeLog("After:" + user.EmployeeId);
                            if (user != null) {
                                StaffName = user.DisplayName;
                                StaffID = user.EmployeeId;

                            }

                        }
                        catch (Exception ex)
                        {
                            writeLog($"Second try: Error - {ex.Message} Inner Exception: {ex.InnerException.Message}");
                        }
                    }

this code is working fine on client's local machine but after upload on client's server it will throw a null reference exception.

any idea. thanks.

I have solved these by my self. I have add two more parameters in below PrincipleContext Constructor. That are Active Directory Domain Username and Password.

using (var context = new PrincipalContext(ContextType.Domain,
                    ConfigurationManager.AppSettings["DomainName"].ToString(),
                    ConfigurationManager.AppSettings["ADUserName"].ToString(),
                    ConfigurationManager.AppSettings["ADPassword"].ToString()))
                {
                    try
                    {
                        writeLog("Before:" + isCheckUserName);
                        writeLog("Context name:" + context.Name);
                        var user = UserPrincipal.FindByIdentity(context, GetCurrentWindowsLogin());

                        writeLog("GetCurrent:" + GetCurrentWindowsLogin());
                        writeLog("After:" + user.EmployeeId);
                        if (user != null)
                        {
                            StaffName = user.DisplayName;
                            StaffID = user.EmployeeId;

                        }

                    }
                    catch (Exception ex)
                    {
                        writeLog($"Second try: Error - {ex.Message} Inner Exception: {ex.InnerException.Message}");
                    }
                }

and changing in IIS Authorization. Set Anonymous Authentication to "Disable", and Set ASP.NET Impersonation to "Enable".