Accessing a Shared File (UNC) From a Remote, Non-Trusted Domain With Credentials
We've run into an interesting situation that needs solving, and my searches have turned up nill. I therefore appeal to the SO community for help.
The issue is this: we have a need to programmatically access a shared file that is not in our domain, and is not within a trusted external domain via remote file sharing / UNC. Naturally, we need to supply credentials to the remote machine.
Typically, one solves this problem in one of two ways:
- Map the file share as a drive and supply the credentials at that time. This is typically done using the
NET USEcommand or the Win32 functions that duplicateNET USE. - Access the file with a UNC path as if the remote computer were on the domain and ensure that the account under which the program runs is duplicated (including password) on the remote machine as a local user. Basically leverage the fact that Windows will automatically supply the current user's credentials when the user attempts to access a shared file.
- Don't use remote file sharing. Use FTP (or some other means) to transfer the file, work on it locally, then transfer it back.
For various and sundry reasons, our security / network architects have rejected the first two approaches. The second approach is obviously a security hole; if the remote computer is compromised, the local computer is now at risk. The first approach is unsatisfactory because the newly mounted drive is a shared resource available to other programs on the local computer during file access by the program. Even though it's quite possible to make this temporary, it's still a hole in their opinion.
They're open to the third option, but the remote network admins insist on SFTP rather than FTPS, and FtpWebRequest only supports FTPS. SFTP is the more firewall-friendly option and there are a couple libraries I could use for that approach, but I'd prefer to reduce my dependencies if I can.
I've searched MSDN for either a managed or a win32 means of using remote file sharing, but I have failed to come up with anything useful.
And so I ask: Is there another way? Did I miss a super-secret win32 function that does what I want? Or must I pursue some variant of option 3?
Answer
The way to solve your problem is to use a Win32 API called WNetUseConnection.
Use this function to connect to a UNC path with authentication, NOT to map a drive.
This will allow you to connect to a remote machine, even if it is not on the same domain, and even if it has a different username and password.
Once you have used WNetUseConnection you will be able to access the file via a UNC path as if you were on the same domain. The best way is probably through the administrative built in shares.
Example: \\computername\c$\program files\Folder\file.txt
Here is some sample C# code that uses WNetUseConnection.
Note, for the NetResource, you should pass null for the lpLocalName and lpProvider. The dwType should be RESOURCETYPE_DISK. The lpRemoteName should be \\ComputerName.
using System;
using System.Runtime.InteropServices ;
using System.Threading;
namespace ExtremeMirror
{
public class PinvokeWindowsNetworking
{
#region Consts
const int RESOURCE_CONNECTED = 0x00000001;
const int RESOURCE_GLOBALNET = 0x00000002;
const int RESOURCE_REMEMBERED = 0x00000003;
const int RESOURCETYPE_ANY = 0x00000000;
const int RESOURCETYPE_DISK = 0x00000001;
const int RESOURCETYPE_PRINT = 0x00000002;
const int RESOURCEDISPLAYTYPE_GENERIC = 0x00000000;
const int RESOURCEDISPLAYTYPE_DOMAIN = 0x00000001;
const int RESOURCEDISPLAYTYPE_SERVER = 0x00000002;
const int RESOURCEDISPLAYTYPE_SHARE = 0x00000003;
const int RESOURCEDISPLAYTYPE_FILE = 0x00000004;
const int RESOURCEDISPLAYTYPE_GROUP = 0x00000005;
const int RESOURCEUSAGE_CONNECTABLE = 0x00000001;
const int RESOURCEUSAGE_CONTAINER = 0x00000002;
const int CONNECT_INTERACTIVE = 0x00000008;
const int CONNECT_PROMPT = 0x00000010;
const int CONNECT_REDIRECT = 0x00000080;
const int CONNECT_UPDATE_PROFILE = 0x00000001;
const int CONNECT_COMMANDLINE = 0x00000800;
const int CONNECT_CMD_SAVECRED = 0x00001000;
const int CONNECT_LOCALDRIVE = 0x00000100;
#endregion
#region Errors
const int NO_ERROR = 0;
const int ERROR_ACCESS_DENIED = 5;
const int ERROR_ALREADY_ASSIGNED = 85;
const int ERROR_BAD_DEVICE = 1200;
const int ERROR_BAD_NET_NAME = 67;
const int ERROR_BAD_PROVIDER = 1204;
const int ERROR_CANCELLED = 1223;
const int ERROR_EXTENDED_ERROR = 1208;
const int ERROR_INVALID_ADDRESS = 487;
const int ERROR_INVALID_PARAMETER = 87;
const int ERROR_INVALID_PASSWORD = 1216;
const int ERROR_MORE_DATA = 234;
const int ERROR_NO_MORE_ITEMS = 259;
const int ERROR_NO_NET_OR_BAD_PATH = 1203;
const int ERROR_NO_NETWORK = 1222;
const int ERROR_BAD_PROFILE = 1206;
const int ERROR_CANNOT_OPEN_PROFILE = 1205;
const int ERROR_DEVICE_IN_USE = 2404;
const int ERROR_NOT_CONNECTED = 2250;
const int ERROR_OPEN_FILES = 2401;
private struct ErrorClass
{
public int num;
public string message;
public ErrorClass(int num, string message)
{
this.num = num;
this.message = message;
}
}
// Created with excel formula:
// ="new ErrorClass("&A1&", """&PROPER(SUBSTITUTE(MID(A1,7,LEN(A1)-6), "_", " "))&"""), "
private static ErrorClass[] ERROR_LIST = new ErrorClass[] {
new ErrorClass(ERROR_ACCESS_DENIED, "Error: Access Denied"),
new ErrorClass(ERROR_ALREADY_ASSIGNED, "Error: Already Assigned"),
new ErrorClass(ERROR_BAD_DEVICE, "Error: Bad Device"),
new ErrorClass(ERROR_BAD_NET_NAME, "Error: Bad Net Name"),
new ErrorClass(ERROR_BAD_PROVIDER, "Error: Bad Provider"),
new ErrorClass(ERROR_CANCELLED, "Error: Cancelled"),
new ErrorClass(ERROR_EXTENDED_ERROR, "Error: Extended Error"),
new ErrorClass(ERROR_INVALID_ADDRESS, "Error: Invalid Address"),
new ErrorClass(ERROR_INVALID_PARAMETER, "Error: Invalid Parameter"),
new ErrorClass(ERROR_INVALID_PASSWORD, "Error: Invalid Password"),
new ErrorClass(ERROR_MORE_DATA, "Error: More Data"),
new ErrorClass(ERROR_NO_MORE_ITEMS, "Error: No More Items"),
new ErrorClass(ERROR_NO_NET_OR_BAD_PATH, "Error: No Net Or Bad Path"),
new ErrorClass(ERROR_NO_NETWORK, "Error: No Network"),
new ErrorClass(ERROR_BAD_PROFILE, "Error: Bad Profile"),
new ErrorClass(ERROR_CANNOT_OPEN_PROFILE, "Error: Cannot Open Profile"),
new ErrorClass(ERROR_DEVICE_IN_USE, "Error: Device In Use"),
new ErrorClass(ERROR_EXTENDED_ERROR, "Error: Extended Error"),
new ErrorClass(ERROR_NOT_CONNECTED, "Error: Not Connected"),
new ErrorClass(ERROR_OPEN_FILES, "Error: Open Files"),
};
private static string getErrorForNumber(int errNum)
{
foreach (ErrorClass er in ERROR_LIST)
{
if (er.num == errNum) return er.message;
}
return "Error: Unknown, " + errNum;
}
#endregion
[DllImport("Mpr.dll")] private static extern int WNetUseConnection(
IntPtr hwndOwner,
NETRESOURCE lpNetResource,
string lpPassword,
string lpUserID,
int dwFlags,
string lpAccessName,
string lpBufferSize,
string lpResult
);
[DllImport("Mpr.dll")] private static extern int WNetCancelConnection2(
string lpName,
int dwFlags,
bool fForce
);
[StructLayout(LayoutKind.Sequential)] private class NETRESOURCE
{
public int dwScope = 0;
public int dwType = 0;
public int dwDisplayType = 0;
public int dwUsage = 0;
public string lpLocalName = "";
public string lpRemoteName = "";
public string lpComment = "";
public string lpProvider = "";
}
public static string connectToRemote(string remoteUNC, string username, string password)
{
return connectToRemote(remoteUNC, username, password, false);
}
public static string connectToRemote(string remoteUNC, string username, string password, bool promptUser)
{
NETRESOURCE nr = new NETRESOURCE();
nr.dwType = RESOURCETYPE_DISK;
nr.lpRemoteName = remoteUNC;
// nr.lpLocalName = "F:";
int ret;
if (promptUser)
ret = WNetUseConnection(IntPtr.Zero, nr, "", "", CONNECT_INTERACTIVE | CONNECT_PROMPT, null, null, null);
else
ret = WNetUseConnection(IntPtr.Zero, nr, password, username, 0, null, null, null);
if (ret == NO_ERROR) return null;
return getErrorForNumber(ret);
}
public static string disconnectRemote(string remoteUNC)
{
int ret = WNetCancelConnection2(remoteUNC, CONNECT_UPDATE_PROFILE, false);
if (ret == NO_ERROR) return null;
return getErrorForNumber(ret);
}
}
}