(PureBasic) Verify FTP SSL Server Certificate

This example demonstrates how to verify the FTP server's certificate and authenticity. The intent is to verify the authenticity of the server before passing a login/password to it.

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IncludeFile "CkFtp2.pb"
IncludeFile "CkCert.pb"

Procedure ChilkatExample()

    ; This example requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

    ftp.i = CkFtp2::ckCreate()
    If ftp.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkFtp2::setCkHostname(ftp, "ftp.myftpserver.com")
    CkFtp2::setCkUsername(ftp, "myUsername")
    CkFtp2::setCkPassword(ftp, "myPassword")

    ; Establish an AUTH SSL secure channel after connection
    ; on the standard FTP port 21.
    CkFtp2::setCkAuthSsl(ftp, 1)

    ; The Ssl property is for establishing an implicit SSL connection
    ; on port 990.  Do not set it.
    CkFtp2::setCkSsl(ftp, 0)

    ; Indicate that the FTP server must have a verifiable SSL certificate.
    ; Do not accept self-signed certs or certificates that are
    ; expired, revoked, or cannot be verified to a root authority:
    CkFtp2::setCkRequireSslCertVerify(ftp, 1)

    ; You may also set a requirement.  In this example,
    ; the certificate's Common Name (CN) must match the
    ; required string exactly:
    CkFtp2::ckSetSslCertRequirement(ftp,"subjectcn","Chilkat Software, Inc.")

    ; Connect and login to the FTP server.
    success.i = CkFtp2::ckConnect(ftp)
    If success <> 1
        Debug CkFtp2::ckLastErrorText(ftp)
        CkFtp2::ckDispose(ftp)
        ProcedureReturn
    Else
        ; LastErrorText contains information even when
        ; successful. This allows you to visually verify
        ; that the secure connection actually occurred.
        Debug CkFtp2::ckLastErrorText(ftp)
    EndIf

    ; After logging on, you may examine the FTP server's cert:
    cert.i
    cert = CkFtp2::ckGetSslServerCert(ftp)
    If CkFtp2::ckLastMethodSuccess(ftp) <> 1
        Debug "No server certificate!"
    Else
        ; Display the distinguished name of the SSL cert.
        Debug CkCert::ckSubjectDN(cert)
    EndIf

    Debug "Secure FTP Channel Established!"

    ; Do whatever you're doing to do ...
    ; upload files, download files, etc...

    success = CkFtp2::ckDisconnect(ftp)


    CkFtp2::ckDispose(ftp)


    ProcedureReturn
EndProcedure