string graphResourceId = "https://graph.windows.net";
string tenantId = "xxx.onmicrosoft.com";
AuthenticationContext authContext = new AuthenticationContext("https://login.microsoftonline.com/xxx.onmicrosoft.com");
ClientCredential credential = new ClientCredential("{clientId}", "{secret}");
string userObjectID = ClaimsPrincipal.Current.FindFirst("http://schemas.microsoft.com/identity/claims/objectidentifier").Value;
AuthenticationResult result = await authContext.AcquireTokenSilentAsync(graphResourceId, credential, new UserIdentifier(userObjectID, UserIdentifierType.UniqueId));
var accessToken = result.AccessToken;


Uri servicePointUri = new Uri(graphResourceId);
Uri serviceRoot = new Uri(servicePointUri, tenantId);

ActiveDirectoryClient graphClient = new ActiveDirectoryClient(serviceRoot, async () => await Task.FromResult(accessToken));

var user = new User();
user.AccountEnabled = true;
user.DisplayName = "testName";
user.UserPrincipalName = "testName@xxx.onmicrosoft.com";
user.MailNickname = "testName";
user.UsageLocation = "US";
user.PasswordProfile = new PasswordProfile
{
    Password = "xxxxxx",
    ForceChangePasswordNextLogin = true
};

await graphClient.Users.AddUserAsync(user);