Authority needed to break outhouse lock (5,4)

I believe the answer is:

privy seal

I'm a little stuck... Click here to teach me more about this clue!

'authority needed to break' is the definition.
I can't judge whether this definition defines the answer.

'outhouse lock' is the wordplay.
'outhouse' becomes 'privy' (synonyms).
'lock' becomes 'seal' (I can't explain this - if you can you should believe this answer much more).
'privy'+'seal'='PRIVY SEAL'

Can you help me to learn more?

(Another definition for privy seal that I've seen is " Mark of authentication on certain royal documents".)

I've seen this clue in the Sydney Morning Herald.

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