Question

I am working on a ASP.NET application using C# that is trying to read some files from a website by logging in and then writing the files on local drive.

I have already passed network credentials to logon to the website by reading the default credentials using –

request.Proxy.Credentials = CredentialCache.DefaultCredentials;

Now i want to store the files on a server directory that requires some credentials to access the location.

Code of logging on to the website –

                string webUrl = "https://web.site.com/";

            string formParams = string.Format("user={0}&password={1}", username, password);

            WebRequest req = WebRequest.Create(webUrl);
            req.ContentType = "application/x-www-form-urlencoded";
            req.Method = "POST";
            req.Proxy.Credentials = CredentialCache.DefaultCredentials;
            byte[] bytes = Encoding.ASCII.GetBytes(formParams);
            req.ContentLength = bytes.Length;
            using (Stream os = req.GetRequestStream())
            {
                os.Write(bytes, 0, bytes.Length);
            }
            WebResponse resp = req.GetResponse();

            cookieHeader = resp.Headers["Set-cookie"];

And the location is \\11.11.11.11\Folder\

How can I pass credentials for accessing that location?
I have learned about impersonation but not getting anything helpful so far. I have credentials that gives access to the location. But how can I do so by using C# code?

Thanks in advance 🙂

Answer 1

You can use the LogonUser API for this. You use the LogonUser function to create a token that represents the WindowsIdentity you want to impersonate. You then create a WindowsIdentity using the token and call Impersonate on the identity. All code that follows runs under the impersonated identity.

Make sure that you always Undo the WindowsImpersonationContext.

[DllImport("advapi32.dll", SetLastError=true)]
public static extern bool LogonUser(string lpszUsername, string lpszDomain, 
                                    string lpszPassword, int dwLogonType, 
                                    int dwLogonProvider, out IntPtr phToken);

[DllImport("advapi32.dll", SetLastError=true)]
public extern static bool DuplicateToken(
    IntPtr ExistingTokenHandle, int SECURITY_IMPERSONATION_LEVEL,
    out IntPtr DuplicateTokenHandle);

[DllImport("kernel32.dll", SetLastError=true)]
static extern bool CloseHandle(IntPtr hHandle);

const int LOGON32_LOGON_INTERACTIVE = 2;
const int LOGON32_PROVIDER_DEFAULT = 0;
IntPtr hToken;
IntPtr hTokenDuplicate;

if (LogonUser(username, domain, password,
              LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, out hToken))
{
    if (DuplicateToken(hToken, 2, out hTokenDuplicate))
    {
        WindowsIdentity windowsIdentity = new WindowsIdentity(hTokenDuplicate);
        WindowsImpersonationContext impersonationContext =
            windowsIdentity.Impersonate();
        try
        {
            // Access files ...
            // ...
        }
        finally
        {
            impersonationContext.Undo();   
            if (hToken != IntPtr.Zero) CloseHandle(hToken);
            if (hTokenDuplicate != IntPtr.Zero) CloseHandle(hTokenDuplicate);
        }
    }
}