Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // 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.

  final ftp = CkFtp2();

  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 = 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.
  ftp.setSslCertRequirement('SubjectCN', 'ftp.example.com');

  try {
    ftp.connect();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Connected; server certificate met the requirement.');

  try {
    ftp.disconnect();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }
}