How do I set the credentials of a a windows service log on?

Question

How do I programmatically set the "Log On" credentials for an arbitrary Windows service using c# (wmi/interop is fine)?

Note, my program is running as an administrator and I need the change to persist (for all subsequent service restarts)

Ideally the method has the following sig:

void SetWindowsServiceCreds(string serviceName, string username, string password) 
{
   // TODO write me
}

Answer 1

[DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool ChangeServiceConfig(IntPtr hService, UInt32 nServiceType, UInt32 nStartType, UInt32 nErrorControl, String lpBinaryPathName, String lpLoadOrderGroup, IntPtr lpdwTagId, String lpDependencies, String lpServiceStartName, String lpPassword, String lpDisplayName);

[DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Auto)]
static extern IntPtr OpenService(IntPtr hSCManager, string lpServiceName, uint dwDesiredAccess);

[DllImport("advapi32.dll", EntryPoint = "OpenSCManagerW", ExactSpelling = true, CharSet = CharSet.Unicode, SetLastError = true)]
internal static extern IntPtr OpenSCManager(
     string machineName,
     string databaseName,
     uint dwAccess);

[DllImport("advapi32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern bool CloseServiceHandle(IntPtr hSCObject);

[DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
public static extern Boolean QueryServiceConfig(IntPtr hService, IntPtr intPtrQueryConfig, UInt32 cbBufSize, out UInt32 pcbBytesNeeded);

[StructLayout(LayoutKind.Sequential)]
public class QUERY_SERVICE_CONFIG
{
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.U4)]
    public UInt32 dwServiceType;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.U4)]
    public UInt32 dwStartType;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.U4)]
    public UInt32 dwErrorControl;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)]
    public String lpBinaryPathName;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)]
    public String lpLoadOrderGroup;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.U4)]
    public UInt32 dwTagID;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)]
    public String lpDependencies;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)]
    public String lpServiceStartName;
    [MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)]
    public String lpDisplayName;
};

private const uint SC_MANAGER_ALL_ACCESS = 0x000F003F;
private const uint SERVICE_QUERY_CONFIG = 0x00001;
private const uint SERVICE_CHANGE_CONFIG = 0x00002;
private const uint SERVICE_NO_CHANGE = 0xffffffff;
private const int ERROR_INSUFFICIENT_BUFFER = 122;

public static void SetWindowsServiceCreds(string serviceName, string username, string password)
{
    IntPtr hManager = IntPtr.Zero;
    IntPtr hService = IntPtr.Zero;
    try
    {
        hManager = OpenSCManager(null, null, SC_MANAGER_ALL_ACCESS);
        if (hManager == IntPtr.Zero)
        {
            ThrowWin32Exception();
        }
        hService = OpenService(hManager, serviceName, SERVICE_QUERY_CONFIG | SERVICE_CHANGE_CONFIG);
        if (hService == IntPtr.Zero)
        {
            ThrowWin32Exception();
        }

        if (!ChangeServiceConfig(hService, SERVICE_NO_CHANGE, SERVICE_NO_CHANGE, SERVICE_NO_CHANGE, null, null, IntPtr.Zero, null, username, password, null))
        {
            ThrowWin32Exception();
        }
    }
    finally
    {
        if (hService != IntPtr.Zero) CloseServiceHandle(hService);
        if (hManager != IntPtr.Zero) CloseServiceHandle(hManager);
    }
}

private static void ThrowWin32Exception()
{
    int error = Marshal.GetLastWin32Error();
    Win32Exception e = new Win32Exception(error);
    throw e;            
}