optionalHeaderValueByName
Optionally extracts the value of the HTTP request header with the given name.
Signature
def optionalHeaderValueByName(headerName: Symbol): Directive1[Option[String]]
def optionalHeaderValueByName(headerName: String): Directive1[Option[String]]
Description
The optionalHeaderValueByName directive is similar to the headerValueByName directive but always extracts an Option value instead of rejecting the request if no matching header could be found.