[tor-bugs] #27549 [Core Tor/Tor]: hs-v3: Refactor the descriptor cookie computation code

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#27549: hs-v3: Refactor the descriptor cookie computation code
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     Reporter:  dgoulet       |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: unspecified
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-hs, refactoring
Actual Points:                |  Parent ID:  #27544
       Points:                |   Reviewer:
      Sponsor:                |
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 These functions have very very similar code for computing
 `hs_desc_build_authorized_client()` and `decrypt_descriptor_cookie()` for
 computing the keys for the client authorization.

 We should refactor this and consolidate since they do the same work on
 both sides (client and service).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27549>
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