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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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const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // 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.

    const ftp = try chilkat.Ftp2.init();
    defer ftp.deinit();

    ftp.setHostname("ftp.example.com");
    ftp.setUsername("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.setPassword("myPassword");

    // Use explicit FTPS (AUTH TLS) on the standard FTP port.
    ftp.setAuthTls(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");

    ftp.connect() catch {
        std.debug.print("{s}\n", .{try ftp.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("Connected; server certificate met the requirement.\n", .{});

    ftp.disconnect() catch {
        std.debug.print("{s}\n", .{try ftp.getLastErrorText(alloc)});
        return;
    };
}