private static BaseEncoding lowerCasedBase16() {
        return lowerCasedBase16;
    }
{@code "tls.proto"} - the current {@linkplain SSLSession#getProtocol() TLS protocol}.
Unavailable if TLS handshake is not finished or the connection is not a TLS connection, such as
{@code "TLSv1.2"}.
core/src/main/java/com/linecorp/armeria/common/logging/BuiltInProperty.java