Work within proper authority (5)
I believe the answer is:
'work' is the definition.
'within proper authority' is the wordplay.
'within' says the answer is hidden in the clue.
'OPERA' is hidden within 'proper authority'.
(Other definitions for opera that I've seen before include "Eg, The Magic Flute" , "Dramatic genre" , "The Magic Flute, say" , "Tosca, for example" , ""Rigoletto", for example" .)