SecurityContext Class
Encapsulates and propagates all security-related data for execution contexts transferred across threads. This class cannot be inherited.
Assembly: mscorlib (in mscorlib.dll)
A SecurityContext object captures all security-related information for a logical thread, including the information contained in the WindowsIdentity and CompressedStack objects. This configuration allows the Windows identity and the security elements on the stack to be propagated automatically when the SecurityContext is copied and transferred across asynchronous threads.
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The common language runtime (CLR) is aware of impersonation operations performed using only managed code, not of impersonation performed outside of managed code, such as through platform invoke to unmanaged code or through direct calls to Win32 functions. Only managed WindowsIdentity objects can flow across asynchronous points, unless the alwaysFlowImpersonationPolicy element has been set to true (<alwaysFlowImpersonationPolicy enabled="true"/>). Setting the alwaysFlowImpersonationPolicy element to true specifies that the Windows identity always flows across asynchronous points, regardless of how impersonation was performed. For more information on flowing unmanaged impersonation across asynchronous points, see <alwaysFlowImpersonationPolicy> Element. |
The SecurityContext is part of the larger ExecutionContext and flows or migrates when the ExecutionContext flows or migrates.
The following code example shows the use of members of the SecurityContext class.
Imports System Imports System.Threading Imports System.Security Imports System.Security.Permissions Imports System.Security.Principal Imports System.Runtime.InteropServices Module Module1 Sub Main() Try Console.WriteLine("Executing the Main method in the primary thread.") Dim fdp As New FileDialogPermission( _ FileDialogPermissionAccess.OpenSave) fdp.Deny() Dim sC As Security.SecurityContext sC = Security.SecurityContext.Capture() ' Do not allow the security context to pass across threads; ' suppress its flow. Dim aFC As AsyncFlowControl aFC = Security.SecurityContext.SuppressFlow() Dim t1 As New Thread(New ThreadStart(AddressOf DemandPermission)) t1.Start() t1.Join() Console.WriteLine("Is the flow suppressed? " & _ Security.SecurityContext.IsFlowSuppressed()) Console.WriteLine("Restore the flow.") aFC.Undo() Console.WriteLine("Is the flow suppressed? " & _ Security.SecurityContext.IsFlowSuppressed()) Dim t2 As New Thread(New ThreadStart(AddressOf DemandPermission)) t2.Start() t2.Join() CodeAccessPermission.RevertDeny() Dim iU As New ImpersonateUser() iU.Impersonate() Dim t5 As New Thread(New ThreadStart(AddressOf CheckIdentity)) t5.Start() t5.Join() Console.WriteLine("Suppress the flow of the Windows identity.") Dim aFC2 As AsyncFlowControl aFC2 = Security.SecurityContext.SuppressFlowWindowsIdentity() Console.WriteLine("Has the Windows identity flow been suppressed? " & _ Security.SecurityContext.IsWindowsIdentityFlowSuppressed()) Dim t6 As New Thread(New ThreadStart(AddressOf CheckIdentity)) Console.WriteLine("Starting the second thread.") t6.Start() t6.Join() Console.WriteLine("Returned from the second thread.") ' Restore the flow of the Windows identity for the impersonated ' user. aFC2.Undo() WriteLine("User name after restoring the Windows identity flow: ") WriteLine(WindowsIdentity.GetCurrent().Name) Console.WriteLine("Undo the impersonation.") iU.Undo() Catch ex As Exception WriteLine(ex.Message) End Try ' Align interface and conclude application. WriteLine(vbCrLf + "This sample completed successfully;" + _ " press Exit to continue.") End Sub ' Test method to be called on a second thread. Sub DemandPermission() Try Console.WriteLine("Executing the DemandPermission method from a" & _ "seperate thread") Dim fDP As New FileDialogPermission( _ FileDialogPermissionAccess.OpenSave) fDP.Demand() Console.WriteLine("FileDialogPermission was successsfully demanded.") Catch e As Exception Console.WriteLine(e.Message) End Try End Sub Sub CheckIdentity() Console.WriteLine("Current user: " & WindowsIdentity.GetCurrent().Name) End Sub Public Class ImpersonateUser Declare Auto Function LogonUser Lib "advapi32.dll" ( _ ByVal lpszUsername As String, _ ByVal lpszDomain As String, _ ByVal lpszPassword As String, _ ByVal dwLogonType As Integer, _ ByVal dwLogonProvider As Integer, _ ByRef phToken As IntPtr) As Boolean Declare Auto Function CloseHandle Lib "kernel32.dll" ( _ ByVal handle As IntPtr) As Boolean Declare Auto Function DuplicateToken Lib "advapi32.dll" ( _ ByVal ExistingTokenHandle As IntPtr, _ ByVal SECURITY_IMPERSONATION_LEVEL As Integer, _ ByRef DuplicateTokenHandle As IntPtr) As Boolean Private Shared tokenHandle As New IntPtr(0) Private Shared dupeTokenHandle As New IntPtr(0) Private Shared impersonatedUser As WindowsImpersonationContext ' If you incorporate this code into a DLL, ' be sure to demand that it runs with FullTrust. <PermissionSetAttribute(SecurityAction.Demand, Name:="FullTrust")> _ Public Sub Impersonate() Try Dim userName, domainName As String ' Use the unmanaged LogonUser function to get the user token for ' the specified user, domain, and password. ' To impersonate a user on this machine, use the local machine ' name for the domain name. domainName = InputBox("Enter the name of the domain to log on to") userName = InputBox("Enter the logon name of the user that " + _ "you wish to impersonate on " + domainName) Const LOGON32_PROVIDER_DEFAULT As Integer = 0 ' Passing this parameter causes LogonUser to create a primary ' token. Const LOGON32_LOGON_INTERACTIVE As Integer = 2 tokenHandle = IntPtr.Zero ' Call LogonUser to obtain a handle to an access token. Dim returnValue As Boolean = LogonUser( _ userName, _ domainName, _ InputBox("Enter the password for " + userName), _ LOGON32_LOGON_INTERACTIVE, _ LOGON32_PROVIDER_DEFAULT, _ tokenHandle) If (returnValue) Then Dim outputMessage As String outputMessage = ("User successfully logged on!" + vbCrLf) outputMessage += ("Windows NT token value: ") outputMessage += (tokenHandle.ToString() + vbCrLf) outputMessage += ("User name before impersonation: ") outputMessage += (WindowsIdentity.GetCurrent().Name + vbCrLf) Dim newId As New WindowsIdentity(tokenHandle) impersonatedUser = newId.Impersonate() outputMessage += ("User name after the impersonation: ") outputMessage += (WindowsIdentity.GetCurrent().Name + vbCrLf) MsgBox(outputMessage) Else Dim ret As Integer = Marshal.GetLastWin32Error() Throw New System.ComponentModel.Win32Exception(ret) End If Catch ex As Exception MsgBox("LogonUser call failed Exception occurred. " & ex.Message) End Try End Sub Public Sub Undo() impersonatedUser.Undo() ' Check the identity. MsgBox("User name restored to : " + _ WindowsIdentity.GetCurrent().Name) ' Free the tokens. If tokenHandle <> IntPtr.Zero Then CloseHandle(tokenHandle) End If End Sub End Class End Module
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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