docs(web): document CORS wildcard rejection + env-gated convention; align to v1.1.3

mw/cors.go

@@ -7,13 +7,23 @@ const (
 	allowedHeaders = "Content-Type, Authorization, X-Request-ID"
 )
 
-// CORS sets cross-origin resource sharing headers for the provided origins.
-// Returns 204 No Content for OPTIONS preflight requests.
-// Pass the outermost origins first; an empty slice is a no-op.
+// CORS sets cross-origin resource sharing headers for the provided origins
+// (exact match; an empty slice is a no-op). Returns 204 No Content for OPTIONS
+// preflight requests.
+//
+// It panics on "*": a wildcard matches no real Origin here, so passing it would
+// silently disable CORS. For allow-all use [CORSAllowAll] (development only). The
+// recommended wiring gates CORS by environment:
+//
+//	var corsMW func(http.Handler) http.Handler
+//	if strings.EqualFold(cfg.AppEnv, "local") {
+//	    corsMW = mw.CORSAllowAll()            // dev: any origin
+//	} else {
+//	    corsMW = mw.CORS(cfg.AllowedOrigins)  // prod: explicit origins
+//	}
 func CORS(origins []string) func(http.Handler) http.Handler {
-	// "*" is a silent no-op here (exact-match only) — reject it loudly at
-	// construction so a misconfigured service fails to boot instead of quietly
-	// blocking every browser. For allow-all, call CORSAllowAll (development only).
+	// "*" would be a silent no-op (exact-match only) — reject it loudly so a
+	// misconfigured service fails to boot instead of quietly blocking browsers.
 	for _, o := range origins {
 		if o == "*" {
 			panic(`mw.CORS: "*" is not a valid origin — list explicit origins, or use CORSAllowAll() for allow-all`)
@@ -46,8 +56,12 @@ func CORS(origins []string) func(http.Handler) http.Handler {
 	}
 }
 
-// CORSAllowAll is a convenience wrapper that allows any origin.
-// Use only in development — never in production.
+// CORSAllowAll allows any origin by reflecting the request Origin (it does not set
+// Access-Control-Allow-Credentials). Development only — never in production.
+//
+// Use it for the local branch of the env-gated CORS convention; use [CORS] with
+// explicit origins everywhere else. Because [CORS] panics on "*", CORSAllowAll — not
+// a "*" in the origins list — is the way to allow all.
 func CORSAllowAll() func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {