For weather for a flight, make a FlightInfoEx call first to get the origin/destination of the flight, then do the Metar(Ex) call with the airport code.
The example URL you specified in your original post is to retrieve the weather for an airport (“MetarEx” is the function call for airport weather), which takes an airport code as argument. See flightaware.com/commercial/fligh … op_MetarEx
It then ask me for username and password.When i fill username and password it should give me results.But its saying :- Authentication Required .What could be the issue behind this.