C# – How to check if user with [UserName] and [Password] is domain administrator of [DomainName] without impersonation


Impersonation example

I can check is user domain administrator with next lines of code:

using (Impersonation im = new Impersonation(UserName, Domain, Password))
    System.Security.Principal.WindowsIdentity identity = System.Security.Principal.WindowsIdentity.GetCurrent();
    bool isDomainAdmin = identity.IsDomainAdmin(Domain, UserName, Password);
    if (!isDomainAdmin)
        //deny access, for example

where IsDomainAdmin – is extension method

public static bool IsDomainAdmin(this WindowsIdentity identity, string domain, string userName, string password)
    Domain d = Domain.GetDomain(new DirectoryContext(DirectoryContextType.Domain, domain, userName, password));

    using (DirectoryEntry de = d.GetDirectoryEntry())
        byte[] domainSIdArray = (byte[])de.Properties["objectSid"].Value;
        SecurityIdentifier domainSId = new SecurityIdentifier(domainSIdArray, 0);
        SecurityIdentifier domainAdminsSId = new SecurityIdentifier(WellKnownSidType.AccountDomainAdminsSid, domainSId);
        WindowsPrincipal wp = new WindowsPrincipal(identity);
        return wp.IsInRole(domainAdminsSId);

But, when method IsDomainAdmin is called, it is trying to write some files to the %LOCALAPPDATA% for impersonated user, and if program is runnig not as administrator, it throws an exception

Could not load file or assembly 'System.DirectoryServices,
Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or
one of its dependencies. Either a required impersonation level was not
provided, or the provided impersonation level is invalid. (Exception
from HRESULT: 0x80070542)

Best Solution

You certainly don't need a user's password to verify if the user is a member of a group. So why don't you just query AD in a straight-forward manner using DirectoryEntry or DirectorySearcher? If you also need to verify that the password supplied is correct you can do that in an additional step using PrincipalContext.ValidateCredentials. (See PrincipalContext.ValidateCredentials Method (String, String)).

static void Main(string[] args) {
    string userDomain = "somedomain";
    string userName = "username";
    string password = "apassword";

    if (IsDomainAdmin(userDomain, userName)) {
        string fullUserName = userDomain + @"\" + userName;
        PrincipalContext context = new PrincipalContext(
            ContextType.Domain, userDomain);
        if (context.ValidateCredentials(fullUserName, password)) {

public static bool IsDomainAdmin(string domain, string userName) {
    string adminDn = GetAdminDn(domain);
    SearchResult result = (new DirectorySearcher(
        new DirectoryEntry("LDAP://" + domain),
        "(&(objectCategory=user)(samAccountName=" + userName + "))",
        new[] { "memberOf" })).FindOne();
    return result.Properties["memberOf"].Contains(adminDn);

public static string GetAdminDn(string domain) {
    return (string)(new DirectorySearcher(
        new DirectoryEntry("LDAP://" + domain),
        "(&(objectCategory=group)(cn=Domain Admins))")