public SELF preflightResponseHeader(CharSequence name, Supplier<?> valueSupplier) {
        requireNonNull(name, "name");
        requireNonNull(valueSupplier, "valueSupplier");
        preflightResponseHeaders.put(HttpHeaderNames.of(name), valueSupplier);
        return self();
    }
Specifies HTTP response headers that should be added to a CORS preflight response.

<p>An intermediary like a load balancer might require that a CORS preflight request
have certain headers set. This enables such headers to be added.

<p>Some values must be dynamically created when the HTTP response is created, for
example the {@code "Date"} response header. This can be accomplished by using a {@link Supplier}
which will have its {@link Supplier#get()} method invoked when the HTTP response is created.

@param name the name of the HTTP header.
@param valueSupplier a {@link Supplier} which will be invoked at HTTP response creation.
@return {@code this} to support method chaining.
core/src/main/java/com/linecorp/armeria/server/cors/AbstractCorsPolicyBuilder.java