[tor-bugs] #30512 [Circumvention/Snowflake]: Enable cache for ACME certificates in broker

[Tor Bug Tracker & Wiki]

#30512: Enable cache for ACME certificates in broker
-----------------------------------------+---------------------------------
     Reporter:  dcf                      |      Owner:  (none)
         Type:  enhancement              |     Status:  new
     Priority:  Medium                   |  Milestone:
    Component:  Circumvention/Snowflake  |    Version:
     Severity:  Normal                   |   Keywords:  arlolra cohosh dcf
                                         |  phw
Actual Points:                           |  Parent ID:
       Points:                           |   Reviewer:
      Sponsor:                           |
-----------------------------------------+---------------------------------
 The websocket server caches its automatic certificates:
 https://gitweb.torproject.org/pluggable-
 transports/snowflake.git/tree/server/server.go?id=d865b7c252d3a7efd789a84757fc2635b1964921#n309
 But the broker does not:
 https://gitweb.torproject.org/pluggable-
 transports/snowflake.git/tree/broker/broker.go?id=d865b7c252d3a7efd789a84757fc2635b1964921#n265

 In #30509 the broker exceeded the Let's Encrypt rate limits and couldn't
 get a new certificate. Implementing a certificate cache will prevent it
 from happening again.

 Once implemented, remember to undo the temporary `--cert` and `--key`
 configuration that was set up in comment:6:ticket:30509. That certificate
 is good for 1 year.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30512>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online