RemoteCertificateValidationCallback Delegate

Represents the method that handles the validation of a remote server's X.509 certificate.

Assembly: System.Net.Primitives.dll

Declaration

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

Remarks

The RemoteCertificateValidationCallback delegate is used by the SslStream class to validate the certificate presented by a remote server during an SSL/TLS handshake. You can provide a custom implementation of this delegate to control how certificates are trusted.

This delegate is assigned to the SslStream.RemoteCertificateValidationCallback property.

When the callback is invoked, the following parameters are passed:

Parameters

Name	Type	Description
`sender`	Object	The object that initiated the callback. This is typically an instance of the SslStream class.
`certificate`	X509Certificate	The certificate presented by the remote server.
`chain`	X509Chain	The X.509 certificate chain associated with the remote certificate.
`sslPolicyErrors`	SslPolicyErrors	A bitwise combination of enumeration values that indicates errors encountered during certificate validation.

Return Value

Type	Description
Boolean	`true` if the certificate is trusted and validation should succeed; otherwise, `false`.

Example

C# Example

The following example shows how to create a custom validation callback that accepts any certificate (for testing purposes only). In production environments, you should implement more robust validation logic.

using System;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Cryptography.X509Certificates;
using System.Text;

public class SslClient
{
    public static void Connect(string host, int port)
    {
        TcpClient client = new TcpClient(host, port);
        using (SslStream sslStream = new SslStream(client.GetStream(), false, new RemoteCertificateValidationCallback(ValidateServerCertificate), null))
        {
            try
            {
                // Authenticate the client and server.
                sslStream.AuthenticateAsClient(host);

                // Do the communication with the server.
                byte[] message = Encoding.UTF8.GetBytes("Hello from client!");
                sslStream.Write(message);

                // Read message from the server.
                byte[] buffer = new byte[2048];
                int bytesRead = sslStream.Read(buffer, 0, buffer.Length);
                Console.WriteLine("Received: {0}", Encoding.UTF8.GetString(buffer, 0, bytesRead));
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error: {ex.Message}");
            }
        }
        client.Close();
    }

    // Custom certificate validation callback
    public static bool ValidateServerCertificate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
    {
        if (sslPolicyErrors == SslPolicyErrors.None)
        {
            // Server certificate is trusted.
            return true;
        }

        // For testing purposes, allow any certificate.
        // **WARNING: Do not use this in production environments.**
        Console.WriteLine($"Certificate error: {sslPolicyErrors}");
        return true; 
    }

    // To run this example:
    // SslClient.Connect("your_server_host", 12345);
}

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