(Swift 3,4,5...) Verify an XML Signature with Multiple References

Demonstrates how to verify an XML digital signature that contains multiple references.

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func chilkatTest() {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // An example of an enveloping XML signature with mulitple references is available at
    // https://www.chilkatsoft.com/exampleData/envelopedMultipleRefs.xml

    // This example will show how to verify the signature and all references, and also how
    // to verify each reference individually.  This is useful to distinguish which part
    // of the XML signature validation failed.  It could be that one or more of the references
    // failed because of a hash computation mismatch.  Or it could be that the signature over
    // the SignedInfo failed.  

    // First, let's grab the sample XML signature.
    let http = CkoHttp()!
    let sbXml = CkoStringBuilder()!
    var success: Bool = http.quickGetSb("https://www.chilkatsoft.com/exampleData/envelopedMultipleRefs.xml", sbContent: sbXml)
    if success != true {
        print("\(http.lastErrorText!)")
        return
    }

    // Load the XML containing the signature to be verified.
    let verifier = CkoXmlDSig()!
    success = verifier.loadSignatureSb(sbXml)
    if success != true {
        print("\(verifier.lastErrorText!)")
        return
    }

    var verifyReferenceDigests: Bool = true

    // The quick way to validate all references and the signature over the SignedInfo
    // is to call VerifySignature with verifyReferenceDigests equal to true.
    var verified: Bool = verifier.verifySignature(verifyReferenceDigests)
    print("Signature and all reference digests verified = \(verified)")

    // Let's pretend the call to VerifySignature returned false.  Something did not validate.
    // Was it one or more of the References that did not hash to the correct value?
    // Or was it the signature over the SignedInfo that failed?
    // We can check just the signature over the SignedInfo by passing false to VerifySignature.
    // This allows us to skip the hashing and checking each Reference.  
    verifyReferenceDigests = false
    var signedInfoVerified: Bool = verifier.verifySignature(verifyReferenceDigests)
    print("Neglecting the reference hashes, the SignedInfo validation result = \(signedInfoVerified)")

    // We can also verify each reference digest separately
    var numRefs: Int = verifier.numReferences.intValue
    var i: Int = 0
    while i < numRefs {
        var refDigestVerified: Bool = verifier.verifyReferenceDigest(i)
        print("Reference \(i) digest verified = \(refDigestVerified)")
        i = i + 1
    }

    // For this sample XML signature with 3 References, we get the following output:

    // Signature and all reference digests verified = True
    // Neglecting the reference hashes, the SignedInfo validation result = True
    // Reference 0 digest verified = True
    // Reference 1 digest verified = True
    // Reference 2 digest verified = Tru

}