(Swift 3,4,5...) Export a Certificate's Private Key to Various Formats

Loads a digital certificate and private key from a PFX file (also known as PKCS#12) and exports the private key to various formats: (1) PKCS8 Encrypted, (2) PKCS8 Encrypted PEM, (3) PKCS8 unencrypted, (4) PKCS8 PEM unencrypted, (5) RSA DER unencrypted, (6) RSA PEM unencrypted, (7) XML.

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func chilkatTest() {
    let cert = CkoCert()!

    // Load from the PFX file
    var pfxFilename: String? = "/Users/chilkat/testData/pfx/chilkat_ssl_pwd_is_test.pfx"
    var pfxPassword: String? = "test"

    // A PFX typically contains certificates in the chain of authentication.
    // The Chilkat cert object will choose the certificate w/
    // private key farthest from the root authority cert.
    // To access all the certificates in a PFX, use the 
    // Chilkat certificate store object instead.
    var success: Bool = cert.loadPfxFile(pfxFilename, password: pfxPassword)
    if success != true {
        print("\(cert.lastErrorText!)")
        return
    }

    // Get the private key...
    var privKey: CkoPrivateKey?
    privKey = cert.exportPrivateKey()
    if cert.lastMethodSuccess == false {
        print("\(cert.lastErrorText!)")
        return
    }

    // Export to various formats:

    var password: String? = "secret"
    var path: String?

    // PKCS8 Encrypted DER
    path = "/Users/chilkat/testData/privkeys/chilkat_pkcs8_enc.der"
    success = privKey!.savePkcs8EncryptedFile(password, path: path)
    if success != true {
        print("\(privKey!.lastErrorText!)")
        privKey = nil
        return
    }

    // PKCS8 Encrypted PEM
    path = "/Users/chilkat/testData/privkeys/chilkat_pkcs8_enc.pem"
    success = privKey!.savePkcs8EncryptedPemFile(password, path: path)
    if success != true {
        print("\(privKey!.lastErrorText!)")
        privKey = nil
        return
    }

    // PKCS8 Unencrypted DER
    path = "/Users/chilkat/testData/privkeys/chilkat_pkcs8.der"
    success = privKey!.savePkcs8File(path)
    if success != true {
        print("\(privKey!.lastErrorText!)")
        privKey = nil
        return
    }

    // PKCS8 Unencrypted PEM
    path = "/Users/chilkat/testData/privkeys/chilkat_pkcs8.pem"
    success = privKey!.savePkcs8PemFile(path)
    if success != true {
        print("\(privKey!.lastErrorText!)")
        privKey = nil
        return
    }

    //  RSA DER (unencrypted)
    path = "/Users/chilkat/testData/privkeys/chilkat_rsa.der"
    success = privKey!.savePkcs1File(path)
    if success != true {
        print("\(privKey!.lastErrorText!)")
        privKey = nil
        return
    }

    // RSA PEM (unencrypted)
    path = "/Users/chilkat/testData/privkeys/chilkat_rsa.pem"
    success = privKey!.savePemFile(path)
    if success != true {
        print("\(privKey!.lastErrorText!)")
        privKey = nil
        return
    }

    // XML (unencrypted)
    path = "/Users/chilkat/testData/privkeys/chilkat.xml"
    success = privKey!.saveXmlFile(path)
    if success != true {
        print("\(privKey!.lastErrorText!)")
        privKey = nil
        return
    }

    privKey = nil

    print("Private key exported to all formats.")

}