hexdigest.swift

private func hexString(_ iterator: Array<UInt8>.Iterator) -> String {
    return iterator.map { String(format: "%02x", $0) }.joined()
}

let exampleVerifier = "kM83K571n5KFW9u29Xu2qSqgoUwep4I2jZw8FGZg4Yr"
let verifierData = exampleVerifier.data(using: .utf8)!

// CommonCrypto implementation
var buffer = [UInt8](repeating: 0, count: Int(CC_SHA256_DIGEST_LENGTH))
_ = verifierData.withUnsafeBytes { CC_SHA256($0.baseAddress, CC_LONG(verifierData.count), &buffer) }
let string1 = hexString(buffer.makeIterator())
let validHashedData = string1.data(using: .utf8)!

// CryptoKit implementation
let hash = SHA256.hash(data: verifierData)
let string2 = hexString(hash.makeIterator())
let invalidHashedData = string2.data(using: .utf8)!

print("\(base64EncodedString(validHashedData))")
print("\(base64EncodedString(invalidHashedData))")