RemoteCertificateValidationCallback Delegate

Verifies the remote Secure Sockets Layer (SSL) certificate used for authentication.

Namespace:  System.Net.Security
Assembly:  System (in System.dll)

public delegate bool RemoteCertificateValidationCallback(
	Object sender,
	X509Certificate certificate,
	X509Chain chain,
	SslPolicyErrors sslPolicyErrors
)

Parameters

sender
Type: System.Object
An object that contains state information for this validation.
certificate
Type: System.Security.Cryptography.X509Certificates.X509Certificate
The certificate used to authenticate the remote party.
chain
Type: System.Security.Cryptography.X509Certificates.X509Chain
The chain of certificate authorities associated with the remote certificate.
sslPolicyErrors
Type: System.Net.Security.SslPolicyErrors
One or more errors associated with the remote certificate.

Return Value

Type: System.Boolean
A Boolean value that determines whether the specified certificate is accepted for authentication.

The delegate's sslPolicyErrors argument contains any certificate errors returned by SSPI while authenticating the client or server. The Boolean value returned by the method invoked by this delegate determines whether the authentication is allowed to succeed.

This delegate is used with the SslStream class.

The following code example implements a method that is invoked by an instance of the RemoteCertificateValidationCallback class. If there are validation errors, this method displays them and returns false, which prevents communication with the unauthenticated server.



// The following method is invoked by the RemoteCertificateValidationDelegate.
public static bool ValidateServerCertificate(
      object sender,
      X509Certificate certificate,
      X509Chain chain,
      SslPolicyErrors sslPolicyErrors)
{
   if (sslPolicyErrors == SslPolicyErrors.None)
        return true;

    Console.WriteLine("Certificate error: {0}", sslPolicyErrors);

    // Do not allow this client to communicate with unauthenticated servers.
    return false;
}


The following code example creates the delegate using the method defined in the preceding code example.


// Create a TCP/IP client socket.
// machineName is the host running the server application.
TcpClient client = new TcpClient(machineName,443);
Console.WriteLine("Client connected.");
// Create an SSL stream that will close the client's stream.
SslStream sslStream = new SslStream(
    client.GetStream(), 
    false, 
    new RemoteCertificateValidationCallback (ValidateServerCertificate), 
    null
    );
// The server name must match the name on the server certificate.
try 
{
    sslStream.AuthenticateAsClient(serverName);
} 
catch (AuthenticationException e)
{
    Console.WriteLine("Exception: {0}", e.Message);
    if (e.InnerException != null)
    {
        Console.WriteLine("Inner exception: {0}", e.InnerException.Message);
    }
    Console.WriteLine ("Authentication failed - closing the connection.");
    client.Close();
    return;
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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