private void assertIsHttps(URI certUrl) {
        if (!"https".equals(certUrl.getScheme())) {
            throw new SdkClientException("SigningCertURL was not using HTTPS: " + certUrl.toString());
        }
    }
The signing cert URL must be HTTPs.
aws-java-sdk-sns/src/main/java/com/amazonaws/services/sns/message/SigningCertUrlVerifier.java