How can I manipulate token privileges in .Net?

I'd like to use C# to determine which privileges are assigned to my process/thread token, and adjust them as necessary. For example, in order for my program to restart the computer, it must first enable the SeShutdownPrivilege privilege.

How can that be done safely from managed code?

This turns out to be non-trivial because there's no built-in mechanism for it. Not only is P/Invoke required, but you must code carefully to make sure that you don't "leak" privileges by enabling them and then not disabling them soon enough (though not an issue if you're restarting the computer).

For a complete code sample with description, read the MSDN magazine article from March 2005 "Manipulate Privileges in Managed Code Reliably, Securely, and Efficiently" by Mark Novak.

Here's the P/Invoke declarations:

using System;
using System.Runtime.InteropServices;
using System.Runtime.ConstrainedExecution;

namespace PrivilegeClass
{
    [Flags]
    internal enum TokenAccessLevels 
    {
        AssignPrimary       = 0x00000001,
        Duplicate           = 0x00000002,
        Impersonate         = 0x00000004,
        Query               = 0x00000008,
        QuerySource         = 0x00000010,
        AdjustPrivileges    = 0x00000020,
        AdjustGroups        = 0x00000040,
        AdjustDefault       = 0x00000080,
        AdjustSessionId     = 0x00000100,

        Read                = 0x00020000 | Query,

        Write               = 0x00020000 | AdjustPrivileges | AdjustGroups | AdjustDefault,

        AllAccess           = 0x000F0000       |
            AssignPrimary    |
            Duplicate        |
            Impersonate      |
            Query            |
            QuerySource      |
            AdjustPrivileges |
            AdjustGroups     |
            AdjustDefault    |
            AdjustSessionId,

        MaximumAllowed      = 0x02000000
    }

    internal enum SecurityImpersonationLevel
    {
        Anonymous = 0,
        Identification = 1,
        Impersonation = 2,
        Delegation = 3,
    }

    internal enum TokenType
    {
        Primary = 1,
        Impersonation = 2,
    }

    internal sealed class NativeMethods
    {
        internal const uint SE_PRIVILEGE_DISABLED           = 0x00000000;
        internal const uint SE_PRIVILEGE_ENABLED            = 0x00000002;

        [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
        internal struct LUID 
        {
            internal uint LowPart;
            internal uint HighPart;
        }

        [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
        internal struct LUID_AND_ATTRIBUTES 
        {
            internal LUID Luid;
            internal uint Attributes;
        }

        [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
        internal struct TOKEN_PRIVILEGE 
        {
            internal uint                PrivilegeCount;
            internal LUID_AND_ATTRIBUTES Privilege;
        }

        internal const string ADVAPI32 = "advapi32.dll";
        internal const string KERNEL32 = "kernel32.dll";

        internal const int ERROR_SUCCESS = 0x0;
        internal const int ERROR_ACCESS_DENIED  = 0x5;
        internal const int ERROR_NOT_ENOUGH_MEMORY = 0x8;
        internal const int ERROR_NO_TOKEN = 0x3f0;
        internal const int ERROR_NOT_ALL_ASSIGNED = 0x514;
        internal const int ERROR_NO_SUCH_PRIVILEGE = 0x521;
        internal const int ERROR_CANT_OPEN_ANONYMOUS = 0x543;

        [DllImport(
             KERNEL32,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern bool CloseHandle(IntPtr handle);

        [DllImport(
             ADVAPI32,
             CharSet=CharSet.Unicode,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern bool AdjustTokenPrivileges (
            [In]     SafeTokenHandle       TokenHandle,
            [In]     bool                  DisableAllPrivileges,
            [In]     ref TOKEN_PRIVILEGE   NewState,
            [In]     uint                  BufferLength,
            [In,Out] ref TOKEN_PRIVILEGE   PreviousState,
            [In,Out] ref uint              ReturnLength);

        [DllImport(
             ADVAPI32,
             CharSet=CharSet.Auto,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern
        bool RevertToSelf();

        [DllImport(
             ADVAPI32,
             EntryPoint="LookupPrivilegeValueW",
             CharSet=CharSet.Auto,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern
        bool LookupPrivilegeValue (
            [In]     string             lpSystemName,
            [In]     string             lpName,
            [In,Out] ref LUID           Luid);

        [DllImport(
             KERNEL32,
             CharSet=CharSet.Auto,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern 
        IntPtr GetCurrentProcess();

        [DllImport(
             KERNEL32,
             CharSet=CharSet.Auto,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern 
            IntPtr GetCurrentThread ();

        [DllImport(
             ADVAPI32,
             CharSet=CharSet.Unicode,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern 
        bool OpenProcessToken (
            [In]     IntPtr              ProcessToken,
            [In]     TokenAccessLevels   DesiredAccess,
            [In,Out] ref SafeTokenHandle TokenHandle);

        [DllImport
             (ADVAPI32,
             CharSet=CharSet.Unicode,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern
        bool OpenThreadToken(
            [In]     IntPtr              ThreadToken,
            [In]     TokenAccessLevels   DesiredAccess,
            [In]     bool                OpenAsSelf,
            [In,Out] ref SafeTokenHandle TokenHandle);

        [DllImport
            (ADVAPI32,
             CharSet=CharSet.Unicode,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern
        bool DuplicateTokenEx(
            [In]    SafeTokenHandle     ExistingToken,
            [In]    TokenAccessLevels   DesiredAccess,
            [In]    IntPtr              TokenAttributes,
            [In]    SecurityImpersonationLevel  ImpersonationLevel,
            [In]    TokenType           TokenType,
            [In,Out] ref SafeTokenHandle NewToken);

        [DllImport
             (ADVAPI32,
             CharSet=CharSet.Unicode,
             SetLastError=true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal static extern
        bool SetThreadToken(
            [In]    IntPtr              Thread,
            [In]    SafeTokenHandle     Token);

        static NativeMethods()
        {
        }
    }
}