TLS/SSL core

// create client instance (Rebex.Net.WebClient or Rebex.Net.HttpRequestCreator)
// ...

// register custom validation event handler
client.ValidatingCertificate += client_ValidatingCertificate;

' create client instance (Rebex.Net.WebClient or Rebex.Net.HttpRequestCreator)
' ...

' register custom validation event handler
AddHandler client.ValidatingCertificate, AddressOf client_ValidatingCertificate

public void client_ValidatingCertificate(object sender, SslCertificateValidationEventArgs e)
{
    // first try to use the default validation (against the Windows certificate store)
    ValidationResult res = e.CertificateChain.Validate(e.ServerName, 0);
    if (res.Valid)
    {
        e.Accept();
        return;
    }

    // get server certificate of the current connection
    Certificate cert = e.CertificateChain[0];

    // check the certificate is already known
    if (trustedThumbprints.Contains(cert.Thumbprint))
    {
        e.Accept();
        return;
    }

    // the certificate is not know yet - show it to user
    Console.WriteLine("Do you trust to the following certificate?");
    Console.WriteLine(" Common name: {0}", cert.GetCommonName());
    Console.WriteLine(" Thumbprint:  {0}", cert.Thumbprint);
    Console.WriteLine(" Expires on:  {0:d}", cert.GetExpirationDate());

    // ask user for the answer
    // ...

    // accept or reject the certificate
    if (userAnswer)
    {
        e.Accept();

        // OPTIONALY store the current certificate as trusted
        trustedThumbprints.Add(cert.Thumbprint);
    }
    else
    {
        e.Reject();
    }
}

Public Sub client_ValidatingCertificate(sender As Object, e As SslCertificateValidationEventArgs)
    ' first try to use the default validation (against the Windows certificate store)
    Dim res As ValidationResult = e.CertificateChain.Validate(e.ServerName, 0)
    If res.Valid Then
        e.Accept()
        Return
    End If

    ' get server certificate of the current connection
    Dim cert As Certificate = e.CertificateChain(0)

    ' check the certificate is already known
    If trustedThumbprints.Contains(cert.Thumbprint) Then
        e.Accept()
        Return
    End If

    ' the certificate is not know yet - show it to user
    Console.WriteLine("Do you trust to the following certificate?")
    Console.WriteLine(" Common name: {0}", cert.GetCommonName())
    Console.WriteLine(" Thumbprint:  {0}", cert.Thumbprint)
    Console.WriteLine(" Expires on:  {0:d}", cert.GetExpirationDate())

    ' ask user for the answer
    ' ...

    ' accept or reject the certificate
    If userAnswer Then
        e.Accept()

        ' OPTIONALY store the current certificate as trusted
        trustedThumbprints.Add(cert.Thumbprint)
    Else
        e.Reject()
    End If
End Sub

// set a certificate request handler
client.Settings.SslClientCertificateRequestHandler = CertificateRequestHandler.StoreSearch;

' set a certificate request handler
client.Settings.SslClientCertificateRequestHandler = CertificateRequestHandler.StoreSearch

// load a certificate chain from a .P12 or .PFX file
CertificateChain certificate = CertificateChain.LoadPfx("mycert.p12", "password");

// set a certificate request handler
client.Settings.SslClientCertificateRequestHandler = CertificateRequestHandler.CreateRequestHandler(certificate);

' load a certificate chain from a .P12 or .PFX file
Dim certificate As CertificateChain = CertificateChain.LoadPfx("mycert.p12", "password")

' set a certificate request handler
client.Settings.SslClientCertificateRequestHandler = CertificateRequestHandler.CreateRequestHandler(certificate)

private class MyCertRequestHandler : ICertificateRequestHandler
{
    // This method is called during TLS/SSL negotiation
    // when the server requests client certificate authentication
    public CertificateChain Request(TlsSocket socket, DistinguishedName[] issuers)
    {
        // provide a certificate loaded from a .pfx/.p12 file
        return CertificateChain.LoadPfx(clientCertPath, clientCertPassword);
    }
}

Private Class MyCertRequestHandler
    Implements ICertificateRequestHandler
    ' This method is called during TLS/SSL negotiation
    ' when the server requests client certificate authentication
    Public Function Request(socket As TlsSocket, issuers As DistinguishedName()) _
                        As CertificateChain _
                        Implements ICertificateRequestHandler.Request
        ' provide a certificate loaded from a .pfx/.p12 file
        Return CertificateChain.LoadPfx(clientCertPath, clientCertPassword)
    End Function
End Class

// set a certificate request handler
client.Settings.SslClientCertificateRequestHandler = new MyCertRequestHandler();

' set a certificate request handler
client.Settings.SslClientCertificateRequestHandler = New MyCertRequestHandler()