Require Specific FTPS Server Certificate Fields

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Demonstrates the Chilkat Ftp2.SetSslCertRequirement method, which adds a required match against the FTP server certificate. The first argument selects the certificate field (such as SubjectCN or IssuerCN) and the second is the required value. It is a void method; a non-matching certificate causes the connection to fail.

Background: Standard TLS validation confirms a certificate is trusted and valid for the hostname, but it does not guarantee you reached the specific server you expect — a form of pinning closes that gap. Requiring a certificate field to match a known value rejects any certificate that does not, defending against a mis-issued or substituted certificate even if it would otherwise pass validation. Multiple requirements can be added, and all must be satisfied.

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#include <C_CkFtp2.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkFtp2 ftp;

    success = FALSE;

    //  Demonstrates the Ftp2.SetSslCertRequirement method, which adds a required match against the FTP
    //  server certificate.  The 1st argument selects the certificate field and the 2nd is the required
    //  value.  It is a void method.

    ftp = CkFtp2_Create();

    CkFtp2_putHostname(ftp,"ftp.example.com");
    CkFtp2_putUsername(ftp,"myFtpLogin");

    //  Normally you would not hard-code the password in source.  You should instead obtain it
    //  from an interactive prompt, environment variable, or a secrets vault.
    CkFtp2_putPassword(ftp,"myPassword");

    //  Use explicit FTPS (AUTH TLS) on the standard FTP port.
    CkFtp2_putAuthTls(ftp,TRUE);

    //  Require that the server certificate's subject common name matches an expected value.  If the
    //  presented certificate does not match, the TLS connection fails.  Supported fields include
    //  SubjectDN, SubjectCN, IssuerDN, IssuerCN, and others.
    CkFtp2_SetSslCertRequirement(ftp,"SubjectCN","ftp.example.com");

    success = CkFtp2_Connect(ftp);
    if (success == FALSE) {
        printf("%s\n",CkFtp2_lastErrorText(ftp));
        CkFtp2_Dispose(ftp);
        return;
    }

    printf("Connected; server certificate met the requirement.\n");

    success = CkFtp2_Disconnect(ftp);
    if (success == FALSE) {
        printf("%s\n",CkFtp2_lastErrorText(ftp));
        CkFtp2_Dispose(ftp);
        return;
    }



    CkFtp2_Dispose(ftp);

    }