Key of father's Golf, say (8)
I believe the answer is:
passport
'key' is the definition.
(both can mean a means of accessing something)
'father's golf say' is the wordplay.
'father's' becomes 'pa's' (pa can mean dad or father).
'golf say' becomes 'sport' (golf is a kind of sport).
'pas'+'sport'='PASSPORT'
'of' is the link.
(Other definitions for passport that I've seen before include "you might need Visa with this" , "Document allowing travel abroad" , "Travel ID" , "Carte blanche" , "that may gain acceptance" .)