Crossword Genius

Writer on computer matters, unknown expert (9)

Ross

I believe the answer is:

'expert' is the definition.
(authority is a kind of expert)

'writer on computer matters unknown' is the wordplay.
'writer' becomes 'author' (synonyms).
'on' is a charade indicator (letters next to each other).
'computer matters' becomes 'it' (abbreviation for Information Technology).
'unknown' becomes 'y' (algebra).
'author'+'it'+'y'='AUTHORITY'

(Other definitions for authority that I've seen before include "Mandate", "Power, influence", "Expert; permission", "Power to expercise control".)

I've seen this clue in The Guardian.