(Swift 3,4,5...) Extract SignatureValue from Signed XML

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Demonstrates how to extract the signature value from signed XML.

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func chilkatTest() {
    // This example will work with the following signed XML, which as been reformatted for readability.

    // <?xml version="1.0" encoding="utf-8"?>
    // <SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
    //     <SOAP-ENV:Header>
    //         <wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" SOAP-ENV:mustUnderstand="1">
    //             <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
    //                 <ds:SignedInfo>
    //                     <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#">
    //                         <InclusiveNamespaces xmlns="http://www.w3.org/2001/10/xml-exc-c14n#" PrefixList="wsse SOAP-ENV"/>
    //                     </ds:CanonicalizationMethod>
    //                     <ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
    //                     <ds:Reference URI="#Body">
    //                         <ds:Transforms>
    //                             <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
    //                         </ds:Transforms>
    //                         <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
    //                         <ds:DigestValue>OwgHPZNfDkXnZsjpfzXqAcT3RV3HzmTsEy2bP44FJ0M=</ds:DigestValue>
    //                     </ds:Reference>
    //                 </ds:SignedInfo>
    //                 <ds:SignatureValue>C+7FWngU....DJFBcdg==</ds:SignatureValue>
    //                 <ds:KeyInfo>
    //                     <ds:KeyValue>
    //                         <ds:RSAKeyValue>
    //                             <ds:Modulus>sXeRhM55P13.....NAcibRw==</ds:Modulus>
    //                             <ds:Exponent>AQAB</ds:Exponent>
    //                         </ds:RSAKeyValue>
    //                     </ds:KeyValue>
    //                 </ds:KeyInfo>
    //             </ds:Signature>
    //         </wsse:Security>
    //     </SOAP-ENV:Header>
    //     <SOAP-ENV:Body xmlns:SOAP-SEC="http://schemas.xmlsoap.org/soap/security/2000-12" SOAP-SEC:id="Body">
    //         <z:FooBar xmlns:z="http://example.com"/>
    //     </SOAP-ENV:Body>
    // </SOAP-ENV:Envelope>

    // -----------------------------------------------------------------------------------------
    // There are a number of ways we can get the contents of the  <ds:SignatureValue>...</ds:SignatureValue>

    var filePath: String? = "qa_data/xml_dsig_testing/sample_to_show_how_to_extract_sig.xml"

    // If you know there will only be a single SignatureValue in the XML, you don't need to parse XML.
    // Just do quick and simple string search..
    // For example:
    let sb = CkoStringBuilder()!
    var success: Bool = sb.loadFile(filePath, charset: "utf-8")
    if success == false {
        print("Failed to load file.")
        return
    }

    var base64Sig: String? = sb.getBetween("SignatureValue>", endMark: "</")
    print("base64Sig = \(base64Sig!)")

    // -----------------------------------------------------------------------------------------
    // If the XML might contain multiple signatures, but the signatures will always be located in the 
    // same place, then you can (beforehand) copy a sample signed XML into Chilkat's online tool
    // at Generate Parsing Code from XML
    // to get the path to the SignatureValue.  For example, the line of code generated for the SignatureValue
    // for the above XML is:
    // string ds_SignatureValue = xml.GetChildContent("SOAP-ENV:Header|wsse:Security|ds:Signature|ds:SignatureValue");

    // So you can simply use that path..
    let xml = CkoXml()!
    success = xml.loadFile(filePath)
    // Assume success..

    base64Sig = xml.getChildContent("SOAP-ENV:Header|wsse:Security|ds:Signature|ds:SignatureValue")
    print("base64Sig = \(base64Sig!)")

    // -----------------------------------------------------------------------------------------
    // Or perhaps you don't know where the signature is located in the XML.
    // You can search for the tag..
    var xSigVal: CkoXml? = xml.search(forTag: xml, tag: "*:SignatureValue")
    if xml.lastMethodSuccess == true {
        print("base64Sig = \(xSigVal!.content!)")
        xSigVal = nil
    }
    else {
        print("No SignatureValue found.")
    }


}