(Swift 3,4,5...) Validate a JWS Using ECDSA P-256 SHA-256

Validates a JSON Web Signature (JWS) that uses ECDSA P-256 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 an ECDSA public key to validate and recover the protected header and payload.

    // We only need a public key for signature validation.  This is the ECDSA public key
    // that is used:

    //      {"kty":"EC", 
    //       "crv":"P-256", 
    //       "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU", 
    //       "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" 
    //      } 

    let sbPubKey = CkoStringBuilder()!
    sbPubKey.append("{\"kty\":\"EC\",")
    sbPubKey.append("\"crv\":\"P-256\",")
    sbPubKey.append("\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\",")
    sbPubKey.append("\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\"")
    sbPubKey.append("}")

    let pubKey = CkoPublicKey()!
    var success: Bool = pubKey.load(from: sbPubKey.getAsString())
    if success != true {
        print("\(pubKey.lastErrorText!)")
        return
    }

    let jws = CkoJws()!

    // Set the ECC public key:
    var signatureIndex: Int = 0
    jws.setPublicKey(signatureIndex, pubKey: pubKey)

    // Load the JWS.
    let sbJws = CkoStringBuilder()!
    sbJws.append("eyJhbGciOiJFUzI1NiJ9")
    sbJws.append(".")
    sbJws.append("eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt")
    sbJws.append("cGxlLmNvbS9pc19yb290Ijp0cnVlfQ")
    sbJws.append(".")
    sbJws.append("DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA")
    sbJws.append("pmWQxfKTUJqPP3-Kg6NU1Q")

    success = jws.loadSb(sbJws)
    if success != true {
        print("\(jws.lastErrorText!)")
        return
    }

    // 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 ECC key was incorrect, the JWS was invalid, or both.")
        return
    }

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

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

    // 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:
    // 	{ 
    // 	  "alg": "ES256"
    // 	}

}