feat(11-03): add the lighthouse realtime package and its Centrifugo driver

- lighthouse: Service/From with realtime.driver selection, RegisterDriver
  registry, null/log/memory drivers, Route/Surface/Mount, users and actors
- centrifugo: HTTP API client (apikey header, 2xx success, no request
  without a key), five-generator HS256 TokenIssuer, TokenHandler with the
  WinterCMS 401/503 bodies
- module README and root modules table row

modules/lighthouse/centrifugo/config.go

@@ -0,0 +1,78 @@
+// Package centrifugo is the Centrifugo driver of lighthouse: an HTTP API
+// client, a connection and subscription token issuer, and the subscribe
+// proxy handler. Import it for its side effect to register the
+// "centrifugo" realtime.driver.
+package centrifugo
+
+import (
+	"strings"
+	"time"
+
+	"git.golem15.com/golem15/summercms/modules/compass"
+	"git.golem15.com/golem15/summercms/modules/lighthouse"
+)
+
+// Default values of the realtime.centrifugo.* keys.
+const (
+	DefaultAPIURL        = "http://127.0.0.1:8001/api"
+	DefaultTokenTTL      = 3600 * time.Second
+	DefaultWSURL         = "/ws"
+	DefaultTokenPath     = "/api/realtime/token"
+	DefaultSubscribePath = "/api/realtime/subscribe"
+)
+
+// Config is the realtime.centrifugo.* configuration.
+type Config struct {
+	// APIURL is the Centrifugo HTTP API base, without a trailing method.
+	APIURL string
+	// APIKey authenticates publishes; empty disables them.
+	APIKey string
+	// TokenSecret signs connection and subscription tokens (HS256); empty
+	// makes the token route answer 503.
+	TokenSecret string
+	// TokenTTL is the lifetime of issued tokens.
+	TokenTTL time.Duration
+	// WSURL is the WebSocket URL the client connects to.
+	WSURL string
+	// ProxySecret is the X-Centrifugo-Secret header value the subscribe
+	// proxy expects; empty denies every subscribe.
+	ProxySecret string
+	// TokenPath and SubscribePath are the mounted route paths.
+	TokenPath     string
+	SubscribePath string
+}
+
+// LoadConfig reads realtime.centrifugo.* from c, filling the defaults.
+// token_ttl is an integer number of seconds or a duration string.
+func LoadConfig(c *compass.Config) Config {
+	cfg := Config{
+		APIURL:        DefaultAPIURL,
+		TokenTTL:      DefaultTokenTTL,
+		WSURL:         DefaultWSURL,
+		TokenPath:     DefaultTokenPath,
+		SubscribePath: DefaultSubscribePath,
+	}
+	if c == nil {
+		return cfg
+	}
+	str := func(key string) string { return strings.TrimSpace(c.String("realtime.centrifugo." + key)) }
+	if v := str("api_url"); v != "" {
+		cfg.APIURL = strings.TrimSuffix(v, "/")
+	}
+	cfg.APIKey = str("api_key")
+	cfg.TokenSecret = str("token_secret")
+	cfg.ProxySecret = str("proxy_secret")
+	if d := lighthouse.DurationSetting(c, "realtime.centrifugo.token_ttl"); d > 0 {
+		cfg.TokenTTL = d
+	}
+	if v := str("ws_url"); v != "" {
+		cfg.WSURL = v
+	}
+	if v := str("token_path"); v != "" {
+		cfg.TokenPath = v
+	}
+	if v := str("subscribe_path"); v != "" {
+		cfg.SubscribePath = v
+	}
+	return cfg
+}