public static List<String> cachedHeaders() {
        return CACHED_HEADERS;
    }
Returns the list of HTTP header names whose corresponding values will be cached, as specified in
{@link #headerValueCacheSpec()}. Only the header value whose corresponding header name is listed in this
flag will be cached. It is not recommended to specify a header with high cardinality, which will defeat
the purpose of caching.

<p>The default value of this flag is {@value DefaultFlagsProvider#CACHED_HEADERS}. Specify the
{@code -Dcom.linecorp.armeria.cachedHeaders=<comma separated list>} JVM option to override the default.
core/src/main/java/com/linecorp/armeria/common/Flags.java