(Swift 3,4,5...) Validate JWS Using RSASSA-PKCS1-v1_5 SHA-256

Validates a JSON Web Signature (JWS) that uses RSASSA-PKCS1-v1_5 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 RSA public key to validate and recover the protected header and payload.

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

    //      {"kty":"RSA", 
    //       "n":"ofgWCuLjybRlzo0tZWJjNiuSfb4p4fAkd_wWJcyQoTbji9k0l8W26mPddx
    //            HmfHQp-Vaw-4qPCJrcS2mJPMEzP1Pt0Bm4d4QlL-yRT-SFd2lZS-pCgNMs
    //            D1W_YpRPEwOWvG6b32690r2jZ47soMZo9wGzjb_7OMg0LOL-bSf63kpaSH
    //            SXndS5z5rexMdbBYUsLA9e-KXBdQOS-UTo7WTBEMa2R2CapHg665xsmtdV
    //            MTBQY4uDZlxvb3qCo5ZwKh9kG4LT6_I5IhlJH7aGhyxXFvUK-DWNmoudF8
    //            NAco9_h9iaGNj8q2ethFkMLs91kzk2PAcDTW9gb54h4FRWyuXpoQ", 
    //       "e":"AQAB"
    //      }

    let sbPubKey = CkoStringBuilder()!
    sbPubKey.append("{\"kty\":\"RSA\",")
    sbPubKey.append("\"n\":\"ofgWCuLjybRlzo0tZWJjNiuSfb4p4fAkd_wWJcyQoTbji9k0l8W26mPddx")
    sbPubKey.append("HmfHQp-Vaw-4qPCJrcS2mJPMEzP1Pt0Bm4d4QlL-yRT-SFd2lZS-pCgNMs")
    sbPubKey.append("D1W_YpRPEwOWvG6b32690r2jZ47soMZo9wGzjb_7OMg0LOL-bSf63kpaSH")
    sbPubKey.append("SXndS5z5rexMdbBYUsLA9e-KXBdQOS-UTo7WTBEMa2R2CapHg665xsmtdV")
    sbPubKey.append("MTBQY4uDZlxvb3qCo5ZwKh9kG4LT6_I5IhlJH7aGhyxXFvUK-DWNmoudF8")
    sbPubKey.append("NAco9_h9iaGNj8q2ethFkMLs91kzk2PAcDTW9gb54h4FRWyuXpoQ\",")
    sbPubKey.append("\"e\":\"AQAB\"")
    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 RSA public key:
    var signatureIndex: Int = 0
    jws.setPublicKey(signatureIndex, pubKey: pubKey)

    // Load the JWS.
    let sbJws = CkoStringBuilder()!
    sbJws.append("eyJhbGciOiJSUzI1NiJ9")
    sbJws.append(".")
    sbJws.append("eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt")
    sbJws.append("cGxlLmNvbS9pc19yb290Ijp0cnVlfQ")
    sbJws.append(".")
    sbJws.append("cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7")
    sbJws.append("AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4")
    sbJws.append("BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K")
    sbJws.append("0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqv")
    sbJws.append("hJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrB")
    sbJws.append("p0igcN_IoypGlUPQGe77Rw")

    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 RSA 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": "RS256"
    // 	}

}