[tor-bugs] #24617 [Core Tor/Tor]: Feature flags for new controller-accessible Tor features

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#24617: Feature flags for new controller-accessible Tor features
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 Reporter:  meejah          |          Owner:  (none)
     Type:  enhancement     |         Status:  new
 Priority:  Medium          |      Milestone:  Tor: 0.3.5.x-final
Component:  Core Tor/Tor    |        Version:
 Severity:  Normal          |     Resolution:
 Keywords:  needs-proposal  |  Actual Points:
Parent ID:                  |         Points:
 Reviewer:                  |        Sponsor:
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Comment (by meejah):

 Another compelling use-case is "v3 onion authentication". Currently,
 txtorcon just hard-codes this as "no auth on v3 onions".

 However, as this feature gets developed it would be nice to have support
 "early" in txtorcon but there's not a great way to tell if the tor we
 connected to actually supports this yet. If txtorcon can query a GETINFO
 or similar (e.g. `GETINFO feature/onion-v3-auth` or similar) I could add
 support "now" and the controller code can make informed decisions about
 whether to even try setting up authentication.

 (Currently, the only option would be to try and see if it fails. However,
 with some of this stuff the "failure mode" is that Tor exits because the
 config is invalid -- e.g. if you're connected to an older Tor and *aren't*
 using ADD_ONION, a SETCONF with invalid config can nuke the whole Tor
 process).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24617#comment:5>
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