optionalHeaderValue
Traverses the list of request headers with the specified function and extracts the first value the function returns as Some(value).
Signature
def optionalHeaderValue[T](f: HttpHeader ⇒ Option[T]): Directive1[Option[T]]
Description
The optionalHeaderValue directive is similar to the headerValue directive but always extracts an Option value instead of rejecting the request if no matching header could be found.