Perl

Require Specific FTPS Server Certificate Fields

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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use strict;
use warnings;
use Chilkat2;

# 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.

my $ftp = Chilkat2::Ftp2->new;

$ftp->Hostname('ftp.example.com');
$ftp->Username('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.
$ftp->Password('myPassword');

# Use explicit FTPS (AUTH TLS) on the standard FTP port.
$ftp->AuthTls(1);

# 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.
$ftp->SetSslCertRequirement('SubjectCN', 'ftp.example.com');

my $success = $ftp->Connect();
if (!$success) {
    print $ftp->LastErrorText, "\n";
    exit;
}

print "Connected; server certificate met the requirement.\n";

$success = $ftp->Disconnect();
if (!$success) {
    print $ftp->LastErrorText, "\n";
    exit;
}