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//------------------------------------------------------------------------------
// <copyright file="ImpersonationContext.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
namespace System.Web {
using System;
using System.Runtime.InteropServices;
using System.Security.Permissions;
using System.Web.Configuration;
using System.Web.Hosting;
using System.Web.Util;
internal class ImpersonationContext : IDisposable {
private HandleRef _savedToken;
private bool _reverted;
private bool _impersonating;
// arg-less ctor creates dummy context
internal ImpersonationContext() {
}
// ctor that takes a token impersonates that token
internal ImpersonationContext(IntPtr token) {
ImpersonateToken(new HandleRef(this, token));
}
// IDisposable pattern
~ImpersonationContext() {
Dispose(false);
}
void IDisposable.Dispose() {
Undo();
}
private void Dispose(bool disposing) {
if (_savedToken.Handle != IntPtr.Zero) {
try {} finally {
UnsafeNativeMethods.CloseHandle(_savedToken.Handle);
_savedToken = new HandleRef(this, IntPtr.Zero);
}
}
}
// impersonate a given token
protected void ImpersonateToken(HandleRef token) {
try {
// first revert
_savedToken = new HandleRef(this, GetCurrentToken());
if (_savedToken.Handle != IntPtr.Zero) {
if (UnsafeNativeMethods.RevertToSelf() != 0) {
_reverted = true;
}
}
// impersonate token if not zero
if (token.Handle != IntPtr.Zero) {
if (UnsafeNativeMethods.SetThreadToken(IntPtr.Zero, token.Handle) == 0) {
throw new HttpException(SR.GetString(SR.Cannot_impersonate));
}
_impersonating = true;
}
}
catch {
RestoreImpersonation();
throw;
}
}
// restore impersonation to the original state
private void RestoreImpersonation() {
// first revert before reimpersonating
if (_impersonating) {
UnsafeNativeMethods.RevertToSelf();
_impersonating = false;
}
// second reimpersonate the orignal saved identity (if exists)
if (_savedToken.Handle != IntPtr.Zero) {
if (_reverted) {
if (UnsafeNativeMethods.SetThreadToken(IntPtr.Zero, _savedToken.Handle) == 0) {
throw new HttpException(SR.GetString(SR.Cannot_impersonate));
}
}
_reverted = false;
}
}
// 'public' version of Dispose
internal void Undo() {
RestoreImpersonation();
// free unmanaged resources
Dispose(true);
System.GC.SuppressFinalize(this);
}
// helper to get the currently impersonated token
private static IntPtr GetCurrentToken() {
IntPtr token = IntPtr.Zero;
if (UnsafeNativeMethods.OpenThreadToken(
UnsafeNativeMethods.GetCurrentThread(),
UnsafeNativeMethods.TOKEN_READ | UnsafeNativeMethods.TOKEN_IMPERSONATE,
true,
ref token) == 0) {
// if the last error is ERROR_NO_TOKEN it is ok, otherwise throw
if (Marshal.GetLastWin32Error() != UnsafeNativeMethods.ERROR_NO_TOKEN) {
throw new HttpException(SR.GetString(SR.Cannot_impersonate));
}
}
return token;
}
// helper to check if there is a current token
internal static bool CurrentThreadTokenExists {
get {
bool impersonating = false;
try {} finally {
IntPtr token = GetCurrentToken();
if (token != IntPtr.Zero) {
impersonating = true;
UnsafeNativeMethods.CloseHandle(token);
}
}
return impersonating;
}
}
}
internal sealed class ProcessImpersonationContext : ImpersonationContext {
internal ProcessImpersonationContext() {
ImpersonateToken(new HandleRef(this, IntPtr.Zero));
}
}
internal sealed class ApplicationImpersonationContext : ImpersonationContext {
internal ApplicationImpersonationContext() {
ImpersonateToken(new HandleRef(this, HostingEnvironment.ApplicationIdentityToken));
}
}
internal sealed class ClientImpersonationContext : ImpersonationContext {
internal ClientImpersonationContext(HttpContext context) {
Start(context, true);
}
internal ClientImpersonationContext(HttpContext context, bool throwOnError) {
Start(context, throwOnError);
}
private void Start(HttpContext context, bool throwOnError) {
IntPtr token = IntPtr.Zero;
try {
if (context != null) {
token = context.ImpersonationToken;
}
else {
// by default use app identity
token = HostingEnvironment.ApplicationIdentityToken;
}
}
catch {
if (throwOnError) {
throw;
}
}
// only impersonate if there is a token
// this is to optimize for the default case of impersonation="false"
// and no UNC identity, when requests run under process identity
if (token != IntPtr.Zero) {
ImpersonateToken(new HandleRef(this, token));
}
}
}
}
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