Use a TLS Client Certificate

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Demonstrates the Chilkat MailMan.SetSslClientCert method, which sets the client-side certificate to use for SSL/TLS connections. This is typically not required — most SSL/TLS connections authenticate the server only. This example loads a client certificate from a PFX and uses it when connecting.

Background: In an ordinary TLS handshake only the server presents a certificate, and the client proves who it is later with a password. Mutual TLS adds a second leg: the client also presents a certificate, so it is authenticated cryptographically at the transport layer. Some corporate or high-security mail servers require this. Because the client must prove possession of the key, the certificate needs its private key — hence loading from a PFX.

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#include <C_CkMailMan.h>
#include <C_CkCert.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkMailMan mailman;
    HCkCert cert;

    success = FALSE;

    //  Demonstrates the MailMan.SetSslClientCert method, which sets the client-side certificate
    //  to use for SSL/TLS connections.  This is typically not required -- most SSL/TLS
    //  connections authenticate the server only.

    mailman = CkMailMan_Create();

    //  Configure the SMTP server connection.
    CkMailMan_putSmtpHost(mailman,"smtp.example.com");
    CkMailMan_putSmtpPort(mailman,465);
    CkMailMan_putSmtpSsl(mailman,TRUE);
    CkMailMan_putSmtpUsername(mailman,"user@example.com");
    CkMailMan_putSmtpPassword(mailman,"myPassword");

    //  Load the client certificate (with its private key) from a PFX file.
    cert = CkCert_Create();
    success = CkCert_LoadPfxFile(cert,"qa_data/certs/client.pfx","pfx_password");
    if (success == FALSE) {
        printf("%s\n",CkCert_lastErrorText(cert));
        CkMailMan_Dispose(mailman);
        CkCert_Dispose(cert);
        return;
    }

    //  Use this certificate to identify the client during the TLS handshake.
    success = CkMailMan_SetSslClientCert(mailman,cert);
    if (success == FALSE) {
        printf("%s\n",CkMailMan_lastErrorText(mailman));
        CkMailMan_Dispose(mailman);
        CkCert_Dispose(cert);
        return;
    }

    success = CkMailMan_VerifySmtpLogin(mailman);
    if (success == FALSE) {
        printf("%s\n",CkMailMan_lastErrorText(mailman));
        CkMailMan_Dispose(mailman);
        CkCert_Dispose(cert);
        return;
    }

    printf("Connected using a TLS client certificate.\n");

    //  Note: The path "qa_data/certs/client.pfx" is a relative local filesystem path,
    //  relative to the current working directory of the running application.


    CkMailMan_Dispose(mailman);
    CkCert_Dispose(cert);

    }