Go on through, with prior authorisation (4,2)
I believe the answer is:
pass by
'go on' is the definition.
(thesaurus)
'through with prior authorisation' is the wordplay.
'through' becomes 'by'.
'with prior' is a charade indicator (letters next to each other) (some letters go before others).
'authorisation' becomes 'pass' (a pass authorises someone to do something).
'by' after 'pass' is 'PASS BY'.
(Other definitions for pass by that I've seen before include "Don't stop to talk to someone" , "Go on and leave alone" , "neglect" , "Leave on one side" , "Ignore, overlook" .)