fix #1428

Tor listeners should never see an STS cap.

Add an undocumented 'hide-sts' key for listeners that hides the STS cap.
This can be used if the listener is secured at layer 3 or 4 (VPNs,
E2E mixnets). It will be necessary to add the relevant IPs to `secure-nets`.

irc/client.go

 	proxiedIP   net.IP
 	rawHostname string
 	isTor       bool
+	hideSTS     bool
 
 	fakelag              Fakelag
 	deferredFakelagCount int
 		realIP:     realIP,
 		proxiedIP:  proxiedIP,
 		isTor:      wConn.Config.Tor,
+		hideSTS:    wConn.Config.Tor || wConn.Config.HideSTS,
 	}
 	client.sessions = []*Session{session}
 

irc/config.go

 	Tor       bool
 	STSOnly   bool `yaml:"sts-only"`
 	WebSocket bool
+	HideSTS   bool `yaml:"hide-sts"`
 }
 
 type PersistentStatus uint
 		SecureNetDefs            []string                        `yaml:"secure-nets"`
 		secureNets               []net.IPNet
 		supportedCaps            *caps.Set
+		supportedCapsWithoutSTS  *caps.Set
 		capValues                caps.Values
 		Casemapping              Casemapping
 		EnforceUtf8              bool         `yaml:"enforce-utf8"`
 		}
 		lconf.RequireProxy = block.TLS.Proxy || block.Proxy
 		lconf.WebSocket = block.WebSocket
+		lconf.HideSTS = block.HideSTS
 		conf.Server.trueListeners[addr] = lconf
 	}
 	return nil
 		return nil, fmt.Errorf("failed to prepare listeners: %v", err)
 	}
 
+	// #1428: Tor listeners should never see STS
+	config.Server.supportedCapsWithoutSTS = caps.NewSet()
+	config.Server.supportedCapsWithoutSTS.Union(config.Server.supportedCaps)
+	config.Server.supportedCapsWithoutSTS.Disable(caps.STS)
+
 	return config, nil
 }
 

irc/handlers.go

 	supportedCaps := config.Server.supportedCaps
 	if client.isSTSOnly {
 		supportedCaps = stsOnlyCaps
+	} else if rb.session.hideSTS {
+		supportedCaps = config.Server.supportedCapsWithoutSTS
 	}
 
 	badCaps := false

irc/utils/proxy.go

 	Tor       bool
 	STSOnly   bool
 	WebSocket bool
+	HideSTS   bool
 }
 
 // read a PROXY header (either v1 or v2), ensuring we don't read anything beyond