Private Sub btnValidateCredentials_Click(sender As Object, e As EventArgs) Handles btnValidateCredentials.Click
    If ValidateCredentials(txtUserName.Text, txtPassword.Text, txtDomain.Text) Then
        lblResultCredentials.Text = "Credentials are valid"
    Else
        lblResultCredentials.Text = "Credentials are NOT valid"
    End If
End Sub


Public Function ValidateCredentials(ByVal pUsername As String, ByVal pPassword As String, ByVal pDomain As String) As Boolean
    Dim blnValid As Boolean = False
    Try
        Using context As New PrincipalContext(ContextType.Domain, pDomain)
            blnValid = context.ValidateCredentials(pUsername, pPassword, ContextOptions.Negotiate)
        End Using
    Catch ex As Exception
        MessageBox.Show($"An exception occured: {ex.Message}")
    End Try
    Return blnValid
End Function

private void btnValidateCredentials_Click(object sender, EventArgs e)
{
    if (ValidateCredentials(txtUserName.Text, txtPassword.Text, txtDomain.Text))
        lblResultCredentials.Text = "Credentials are valid";
    else
        lblResultCredentials.Text = "Credentials are NOT valid";
}

public bool ValidateCredentials(string pUsername, string pPassword, string pDomain)
{
    bool blnValid = false;
    try
    {
        using (PrincipalContext context = new PrincipalContext(ContextType.Domain, pDomain))
        {
            blnValid = context.ValidateCredentials(pUsername, pPassword, ContextOptions.Negotiate);
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show($"An exception occured: {ex.Message}");
    }
    return blnValid;
}

Private Sub btnGetGroups_Click(sender As Object, e As EventArgs) Handles btnGetGroups.Click
    lstGroups.Items.Clear()

    Dim groups As PrincipalSearchResult(Of Principal) = GetUserGroups(txtUserName.Text, txtPassword.Text, txtDomain.Text)
    For Each result As Principal In groups
        If TypeOf result Is GroupPrincipal Then
            Dim gp As GroupPrincipal = DirectCast(result, GroupPrincipal)
            If gp IsNot Nothing AndAlso gp.IsSecurityGroup Then
                lstGroups.Items.Add($"Security Group: {gp.Name}")
            Else
                lstGroups.Items.Add($"Other Group : {result.DistinguishedName}")
            End If
        Else
            lstGroups.Items.Add($"Other Group : {result.DistinguishedName}")
        End If
    Next
End Sub

Private Function GetUserGroups(ByVal pUsername As String, ByVal pPassword As String, ByVal pDomain As String) As PrincipalSearchResult(Of Principal)
    Dim objContext As New PrincipalContext(ContextType.Domain, pDomain, pUsername, pPassword)
    Dim objUser As UserPrincipal = UserPrincipal.FindByIdentity(objContext, IdentityType.SamAccountName, pUsername)

    Return objUser.GetAuthorizationGroups()
    'Return objUser.GetGroups()
End Function

private void btnGetGroups_Click(object sender, EventArgs e)
{
    lstGroups.Items.Clear();

    PrincipalSearchResult<Principal> groups = GetUserGroups(txtUserName.Text, txtPassword.Text, txtDomain.Text);
    foreach (Principal result in groups)
    {
        if (result is GroupPrincipal)
        {
            GroupPrincipal gp = (GroupPrincipal)result;
            if (gp != null && gp.IsSecurityGroup != null && gp.IsSecurityGroup.Value)
                lstGroups.Items.Add($"Security Group: {gp.Name}");
            else
                lstGroups.Items.Add($"Other Group : {result.DistinguishedName}");
        }
        else
            lstGroups.Items.Add($"Other Group : {result.DistinguishedName}");
    }
}

private PrincipalSearchResult<Principal> GetUserGroups(string pUsername, string pPassword, string pDomain)
{
    PrincipalContext objContext = new PrincipalContext(ContextType.Domain, pDomain, pUsername, pPassword);
    UserPrincipal objUser = UserPrincipal.FindByIdentity(objContext, IdentityType.SamAccountName, pUsername);

    return objUser?.GetAuthorizationGroups();
    //return objUser?.GetGroups();
}

Private Sub btnValidateGroup_Click(sender As Object, e As EventArgs) Handles btnValidateGroup.Click
    lblResultGroup.Text = ValidateGroup(txtUserName.Text, txtPassword.Text, txtDomain.Text, txtGroup.Text)
End Sub

Public Function ValidateGroup(ByVal pUsername As String, ByVal pPassword As String, ByVal pDomain As String, ByVal pGroupName As String) As String
    If String.IsNullOrWhiteSpace(pUsername) OrElse String.IsNullOrWhiteSpace(pPassword) OrElse String.IsNullOrWhiteSpace(pDomain) OrElse String.IsNullOrWhiteSpace(pGroupName) Then
        Return "Fill the required fields first."
    End If

    Try
        Dim objContext As New PrincipalContext(ContextType.Domain, pDomain, pUsername, pPassword)
        Dim objUser As UserPrincipal = UserPrincipal.FindByIdentity(objContext, IdentityType.SamAccountName, pUsername)
        If objUser Is Nothing Then
            Return "User cannot be found"
        Else
            Dim objGroup As GroupPrincipal = GroupPrincipal.FindByIdentity(objContext, pGroupName)
            If objGroup Is Nothing Then
                Return "Group does not exist"
            Else
                Dim objGroups As PrincipalSearchResult(Of Principal) = objUser.GetAuthorizationGroups()
                Dim groupResult As Principal = objGroups.Where(Function(x) x.Name.Trim().ToUpper() = pGroupName.Trim().ToUpper()).FirstOrDefault()

                If groupResult Is Nothing Then
                    Return "User is NOT member of the group"
                Else
                    Return "User is member of the group"
                End If
            End If
        End If
    Catch ex As Exception
        Return $"Exception occured: {ex.Message}"
    End Try
End Function

private void btnValidateGroup_Click(object sender, EventArgs e)
{
    lblResultGroup.Text = ValidateGroup(txtUserName.Text, txtPassword.Text, txtDomain.Text, txtGroup.Text);
}

public string ValidateGroup(string pUsername, string pPassword, string pDomain, string pGroupName)
{
    if (string.IsNullOrWhiteSpace(pUsername) || string.IsNullOrWhiteSpace(pPassword) || string.IsNullOrWhiteSpace(pDomain) || string.IsNullOrWhiteSpace(pGroupName))
        return "Fill the required fields first.";

    try
    {
        PrincipalContext objContext = new PrincipalContext(ContextType.Domain, pDomain, pUsername, pPassword);
        UserPrincipal objUser = UserPrincipal.FindByIdentity(objContext, IdentityType.SamAccountName, pUsername);
        if (objUser == null)
            return "User cannot be found";
        else
        {
            GroupPrincipal objGroup = GroupPrincipal.FindByIdentity(objContext, pGroupName);
            if (objGroup == null)
                return "Group does not exist";
            else
            {
                PrincipalSearchResult<Principal> objGroups = objUser.GetAuthorizationGroups();
                Principal groupResult = objGroups.Where(x => x.Name.Trim().ToUpper() == pGroupName.Trim().ToUpper()).FirstOrDefault();
                if (groupResult == null)
                    return "User is NOT member of the group";
                else
                    return "User is member of the group";
            }
        }
    }
    catch (Exception ex)
    {
        return $"Exception occured: {ex.Message}";
    }
}