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Access a server file using impersonation

Posted on 2006-06-19
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Last Modified: 2008-08-26
I have to access an internal file from a web application and need to use impersonation to get access to the server.

I have not been sucessful so far, and the "help" files for .NET are somewhat lacking...

it's an asp.Net application with C# code behind.

Thank you,

Michelle
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Question by:mnp13
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LVL 12

Expert Comment

by:sumix
ID: 16940049
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Author Comment

by:mnp13
ID: 17099544
please leave it active, I am still working on the project. thank you.
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Author Comment

by:mnp13
ID: 17156530
It's not working and not giving me an error message or any indication of why...

it throws me to the "catch" at this line: impersonationContext =
                              ((System.Security.Principal.WindowsIdentity)User.Identity).Impersonate();
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LVL 96

Expert Comment

by:Bob Learned
ID: 17159369
Can you show me how you are using this code?

Bob
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Author Comment

by:mnp13
ID: 17160832
I'll post the section of code I"m useing on Monday, as it is on my work computer. Thanks!
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Author Comment

by:mnp13
ID: 17167690
using System.Security.Principal;

...code...


                        System.Security.Principal.WindowsImpersonationContext impersonationContext;
                        impersonationContext =
                              ((System.Security.Principal.WindowsIdentity)User.Identity).Impersonate();
                  if (servPath.Equals("Null"))
                  {
                        this.hypServPDF.Enabled = false;
                        this.hypServPDF.Text = "not available";
                  }
                  else
                  {


                        this.hypServPDF.Enabled = true;
                        this.hypServPDF.Text = "Download";
                        this.hypServPDF.NavigateUrl = servPath.ToString();
                        this.hypServPDF.Target = "bill";



                  }
                        impersonationContext.Undo();
                  
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LVL 96

Expert Comment

by:Bob Learned
ID: 17189742
Here is a class converted from VB.NET (untested):

using System;
using System.Runtime.InteropServices;
using System.Security.Principal;
using System.Security.Permissions;

public class WindowsImpersonator
{

  [DllImport("advapi32.dll", CharSet=CharSet.Auto)]
  private static extern bool LogonUser(string lpszUsername, string lpszDomain, string lpszPassword, int dwLogonType, int dwLogonProvider, ref IntPtr phToken);

  [DllImport("kernel32.dll")]
  private static extern int FormatMessage(int dwFlags, ref IntPtr lpSource, int dwMessageId, int dwLanguageId, ref string lpBuffer, int nSize, ref IntPtr Arguments);

  [DllImport("kernel32.dll", CharSet=CharSet.Auto)]
  private static extern bool CloseHandle(IntPtr handle);

  [DllImport("advapi32.dll", CharSet=CharSet.Auto)]
  private static extern bool DuplicateToken(IntPtr ExistingTokenHandle, int SECURITY_IMPERSONATION_LEVEL, ref IntPtr DuplicateTokenHandle);

  private WindowsImpersonationContext m_impersonatedUser;

  private static string GetErrorMessage(int errorCode)
  {
    int FORMAT_MESSAGE_ALLOCATE_BUFFER = 256;
    int FORMAT_MESSAGE_IGNORE_INSERTS = 512;
    int FORMAT_MESSAGE_FROM_SYSTEM = 4096;

    int messageSize = 255;
    string lpMsgBuf = "";
    int dwFlags = FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS;

    IntPtr ptrlpSource = IntPtr.Zero;
    IntPtr prtArguments = IntPtr.Zero;

    int retVal = FormatMessage(dwFlags, ref ptrlpSource, errorCode, 0, ref lpMsgBuf, messageSize, ref prtArguments);
    if (0 == retVal)
    {
      throw new Exception("Failed to format message for error code " + errorCode.ToString() + ". ");
    }
    return lpMsgBuf;
  }

  public void Impersonate(string domainName, string userName, string password)
  {
    const int LOGON32_PROVIDER_DEFAULT = 0;
    const int LOGON32_LOGON_INTERACTIVE = 2;
    const int SecurityImpersonation = 2;
    IntPtr tokenHandle = IntPtr.Zero;
    IntPtr dupeTokenHandle = IntPtr.Zero;
    try
    {
      bool returnValue = LogonUser(userName, domainName, password, LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, ref tokenHandle);
      if (!returnValue)
      {
        int ret = Marshal.GetLastWin32Error();
        throw new Exception(string.Format("Error: [{0}] {1}", ret, GetErrorMessage(ret)));
      }
      bool retVal = DuplicateToken(tokenHandle, SecurityImpersonation, ref dupeTokenHandle);
      if (!retVal)
      {
        CloseHandle(tokenHandle);
        throw new Exception("Exception thrown in trying to duplicate token.");
      }
      WindowsIdentity newId = new WindowsIdentity(dupeTokenHandle);
      m_impersonatedUser = newId.Impersonate();
      if (tokenHandle != IntPtr.Zero)
      {
        CloseHandle(tokenHandle);
      }
      if (dupeTokenHandle != IntPtr.Zero)
      {
        CloseHandle(dupeTokenHandle);
      }
    }
    catch (Exception ex)
    {
      Console.WriteLine(("Exception occurred. " + ex.Message));
    }
  }

  public void Undo()
  {
    m_impersonatedUser.Undo();
  }

  public string CurrentName
  {
    get { return WindowsIdentity.GetCurrent().Name; }
  }

}

Bob
0
 

Author Comment

by:mnp13
ID: 17189883
That is about 10 miles over my head. where do I put that, and where do I put the file path it is suppoed to be accessing?
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LVL 96

Accepted Solution

by:
Bob Learned earned 500 total points
ID: 17191139
Sorry for the great distance.

Here are the steps:

1) Copy/paste that code into a class module

2) Create an instance of the class:

   WindowsImpersonator alias = new WindowsImpersonator();

3) Impersonate someone:

    alias.Impersonate("domain", "user", "password");

4) When your done Undo:

    alias.Undo();

5) The current name is here:

    string currentName = alias.CurrentName;

Bob
0
 

Author Comment

by:mnp13
ID: 17192855
ok, I'll give it a go...

I'm off of work until Monday, but I will try it and repond then.
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