Code:
/ FX-1434 / FX-1434 / 1.0 / untmp / whidbey / REDBITS / ndp / fx / src / xsp / System / Web / ImpersonationContext.cs / 2 / ImpersonationContext.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------------- 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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