private boolean attemptUpgrade() {
        switch (httpPreference) {
            case HTTP1_REQUIRED:
                return false;
            case HTTP2_PREFERRED:
                assert remoteAddress != null;
                return !SessionProtocolNegotiationCache.isUnsupported(remoteAddress, H2C);
            case HTTP2_REQUIRED:
                return true;
            default:
                // Should never reach here.
                throw new Error();
        }
    }
Configures the specified {@link SslHandler} with common settings.
core/src/main/java/com/linecorp/armeria/client/HttpClientPipelineConfigurator.java