Sanction address as part of key-ring (5,2)

'sanction' is the definition.
(I've seen this in another clue)

'address as part of key-ring' is the wordplay.
'address' becomes 'greet' (greeting is a kind of addressing).
'as part of' indicates putting letters inside.
'key' becomes 'A' (musical key).
'ring' becomes 'O' (O is the shape of a ring).
'a'+'o'='ao'
'greet' inserted within 'ao' is 'AGREE TO'.