`System.Net.Security.NegotiateStream.AuthenticateAsClient Method`

Authenticates a client. This method attempts to establish a secure stream using the Negotiate security package.

Syntax

public override void AuthenticateAsClient(
    CredentialCache credentialCache,
    ProtectionLevel requiredProtectionLevel,
    bool leaveStreamOpen
)

public override void AuthenticateAsClient(
    TokenImpersonationLevel requiredImpersonationLevel,
    bool leaveStreamOpen
)

public override void AuthenticateAsClient(
    string targetName,
    bool leaveStreamOpen
)

public override void AuthenticateAsClient(
    string targetName,
    CredentialCache credentialCache,
    ProtectionLevel requiredProtectionLevel,
    bool leaveStreamOpen
)

Parameters

credentialCache A CredentialCache object that contains the client credentials.

requiredProtectionLevel One of the ProtectionLevel enumeration values that specifies the level of protection the client requires.

leaveStreamOpen true to leave the underlying stream open after the authentication is complete; otherwise, false.

requiredImpersonationLevel One of the TokenImpersonationLevel enumeration values that specifies the impersonation level required.

targetName The name of the target service principal name (SPN).

Remarks

The AuthenticateAsClient method is used to initiate the authentication process for a client. It negotiates a security context with a server using the Negotiate security package. The Negotiate package attempts to use Kerberos and then falls back to NTLM if Kerberos is not available.

When you call this method, the NegotiateStream object attempts to obtain credentials and establish a secure channel. The specific overload you use determines how credentials and other security settings are provided.

If leaveStreamOpen is true, the underlying stream remains open after authentication, allowing you to continue sending and receiving data. If false, the stream is closed.

Exceptions

ArgumentNullException credentialCache is null.

ArgumentException targetName is null or empty.

InvalidOperationException The stream is already authenticated or has been closed.

AuthenticationException An error occurred during authentication.

Example


using System;
using System.Net;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Authentication;
using System.Text;

public class ClientExample
{
    public static void Main(string[] args)
    {
        string serverName = "your_server_hostname"; // Replace with actual server hostname
        int port = 12345; // Replace with actual server port

        try
        {
            TcpClient client = new TcpClient(serverName, port);
            using (NetworkStream networkStream = client.GetStream())
            {
                // Use NegotiateStream for client authentication
                // Example using targetName and default settings
                using (NegotiateStream negotiateStream = new NegotiateStream(networkStream, true))
                {
                    // Authenticate as a client
                    // Specify the target SPN (e.g., "HTTP/your_server_hostname")
                    // or null to let NegotiateStream determine it if possible.
                    // For Kerberos, targetName is crucial. For NTLM, it's often optional.
                    negotiateStream.AuthenticateAsClient("HTTP/" + serverName, true);

                    Console.WriteLine("Client authentication successful!");

                    // Now you can send and receive data securely
                    byte[] message = Encoding.UTF8.GetBytes("Hello, secure server!");
                    negotiateStream.Write(message, 0, message.Length);
                    Console.WriteLine("Sent: Hello, secure server!");

                    byte[] buffer = new byte[1024];
                    int bytesRead = negotiateStream.Read(buffer, 0, buffer.Length);
                    string response = Encoding.UTF8.GetString(buffer, 0, bytesRead);
                    Console.WriteLine("Received: " + response);
                }
            }
            client.Close();
        }
        catch (Exception ex)
        {
            Console.WriteLine("An error occurred: " + ex.Message);
        }
    }
}

System.Net.Security.NegotiateStream.AuthenticateAsClient Method