Tuesday, September 14, 2010

how to provide functionality to a Windows user based on the user rights that have been granted to the Windows user account.

You can design the Windows Form to accept the user name and password at runtime by using TextBox controls. Then, you can make the application verify the Windows user's user rights when the Windows user clicks a Button control. To do this, follow these steps:

1. Open form
2. from Toolbox,add two textbox to you form.
3. Add a button on form.
4. add a form2 in application
5. Add a Button control to the Form2 form.
6. add a label control on form2..
7. Right-click the Label1 Label control, and then click Properties.
8. In the Properties window, set the Size property to 200, 56.
9. Double-click the Button1 Button control, and then add the following code to the Button1_Click event handler:

Dim firstnum, secondnum, result As Integer
firstnum = InputBox("Enter the first number")
secondnum = InputBox("Enter the second number")
result = firstnum + secondnum
MessageBox.Show("The sum of the two numbers is:" & result)

Write code to validate the Windows user in your Visual Basic .NET application
You can use the LogonUser Win32 API to verify the user name and password. The LogonUser function is declared in the Advapi32.dll library. You can call the LogonUser function from your Visual Basic .NET application by using the Declare statement.

You must pass the domain name, the user name, and the password to the LogonUser function. The LogonUser function validates the user by using these parameters and then returns a Boolean value. If the function succeeds, you receive a handle to a token that represents the Windows user. The WindowsIdentity object uses this token to represent the Windows user in your Visual Basic .NET or Visual Basic 2005 application. The WindowsPrincipal object uses this WindowsIdentity object to verify the Windows user's user rights.

To write code that implements validation in your Visual Basic .NET or Visual Basic 2005 application, follow these steps:

1. In Solution Explorer, right-click Form1.vb, and then click View Code.
2. Add the following code at the top of the Form1 form:

Imports System.Security.Principal
Imports System.Security.Permissions
Imports System.Runtime.InteropServices
Imports System.Environment

3. Locate the following code:

End Class

4. Add the following code before the code that you located in step 3:

'The LogonUser function tries to log on to the local computer
'by using the specified user name. The function authenticates
'the Windows user with the password provided.
Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As [String], _
ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer, _
ByRef phToken As IntPtr) As Boolean

'The FormatMessage function formats a message string that is passed as input.
Public Shared Function FormatMessage(ByVal dwFlags As Integer, ByRef lpSource As IntPtr, _
ByVal dwMessageId As Integer, ByVal dwLanguageId As Integer, ByRef lpBuffer As [String], _
ByVal nSize As Integer, ByRef Arguments As IntPtr) As Integer
End Function

'The CloseHandle function closes the handle to an open object such as an Access token.
Public Declare Auto Function CloseHandle Lib "kernel32.dll" (ByVal handle As IntPtr) As Boolean

5. Locate the following code:

End Class

6. Add the following code before the code that you located in step 5:

'The GetErrorMessage function formats and then returns an error message
'that corresponds to the input error code.
Public Shared Function GetErrorMessage(ByVal errorCode As Integer) As String

Dim msgSize As Integer = 255
Dim lpMsgBuf As String

Dim lpSource As IntPtr = IntPtr.Zero
Dim lpArguments As IntPtr = IntPtr.Zero
'Call the FormatMessage function to format the message.
Dim returnVal As Integer = FormatMessage(dwFlags, lpSource, errorCode, 0, lpMsgBuf, _
msgSize, lpArguments)
If returnVal = 0 Then
Throw New Exception("Failed to format message for error code " + errorCode.ToString() + ". ")
End If
Return lpMsgBuf
End Function

7. In Solution Explorer, right-click Form1.vb, and then click View Designer.
8. Double-click the Button1 Button control, and then add the following code to the Button1_Click event handler:

Dim tokenHandle As New IntPtr(0)

Dim UserName, MachineName, Pwd As String
'The MachineName property gets the name of your computer.
MachineName = System.Environment.MachineName
UserName = TextBox1.Text
Pwd = TextBox2.Text
Dim frm2 As New Form2
tokenHandle = IntPtr.Zero
'Call the LogonUser function to obtain a handle to an access token.
Dim returnValue As Boolean = LogonUser(UserName, MachineName, Pwd, LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, tokenHandle)

If returnValue = False Then
'This function returns the error code that the last unmanaged function returned.
Dim ret As Integer = Marshal.GetLastWin32Error()
Dim errmsg As String = GetErrorMessage(ret)
frm2.Label1.Text = errmsg
frm2.Button1.Visible = False
'Create the WindowsIdentity object for the Windows user account that is
'represented by the tokenHandle token.
Dim newId As New WindowsIdentity(tokenHandle)
Dim userperm As New WindowsPrincipal(newId)
'Verify whether the Windows user has administrative credentials.
If userperm.IsInRole(WindowsBuiltInRole.Administrator) Then
frm2.Button1.Text = "Add Numbers"
frm2.Label1.Text = "Click this button to add two numbers"
frm2.Label1.Text = " You do not have administrative credentials."
frm2.Button1.Visible = False
End If
End If

'Free the access token.
If Not System.IntPtr.op_Equality(tokenHandle, IntPtr.Zero) Then
End If
Catch ex As Exception
MessageBox.Show("Exception occurred. " + ex.Message)
End Try

Back to the top
Verify that your Visual Basic .NET application works
To verify that the validation has completed correctly, follow these steps:

1. On the Build menu, click Build Solution.
2. On the Debug menu, click Start.
3. In the TextBox1 box, type a user name.
4. In the TextBox2 box, type a password.
5. Click Validate User.


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