(Swift 3,4,5...) Validate JWS Using HMAC SHA-256

Validates a JSON Web Signature (JWS) using HMAC SHA-256.

Note: This example requires Chilkat v9.5.0.66 or greater.

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

    // Note: This example requires Chilkat v9.5.0.66 or greater.

    // This example takes a JSON signature in compact serialization format,
    // and uses a MAC key to validate and recover the protected header and payload.

    let jws = CkoJws()!

    // Set the HMAC key:
    var hmacKey: String? = "AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow"
    var signatureIndex: Int = 0
    jws.setMacKey(signatureIndex, key: hmacKey, encoding: "base64url")

    // Load the JWS.
    var jwsCompact: String? = "eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ.dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"
    var success: Bool = jws.load(jwsCompact)

    // Validate the 1st (and only) signature at index 0..
    var v: Int = jws.validate(signatureIndex).intValue
    if v < 0 {
        // Perhaps Chilkat was not unlocked or the trial expired..
        print("Method call failed for some other reason.")
        print("\(jws.lastErrorText!)")
        return
    }

    if v == 0 {
        print("Invalid signature.  The MAC key was incorrect, the JWS was invalid, or both.")
        return
    }

    // If we get here, the signature was validated..
    print("Signature validated.")

    // Recover the original content:
    print("Recovered content:")
    print("\(jws.getPayload("utf-8")!)")

    // Examine the protected header:
    var joseHeader: CkoJsonObject? = jws.getProtectedHeader(signatureIndex)
    if jws.lastMethodSuccess != true {
        print("No protected header found at the given index.")
        return
    }

    joseHeader.emitCompact = false

    print("Protected (JOSE) header:")
    print("\(joseHeader!.emit()!)")
    joseHeader = nil

    // Output:

    // 	Signature validated.
    // 	Recovered content:
    // 	{"iss":"joe",
    // 	 "exp":1300819380,
    // 	 "http://example.com/is_root":true}
    // 	Protected (JOSE) header:
    // 	{ 
    // 	  "typ": "JWT",
    // 	  "alg": "HS256"
    // 	}

}