feat(安全): 强化安全策略与配置校验

- 增加 CORS/CSP/安全响应头与代理信任配置

- 引入 URL 白名单与私网开关，校验上游与价格源

- 改善 API Key 处理与网关错误返回

- 管理端设置隐藏敏感字段并优化前端提示

- 增加计费熔断与相关配置示例

测试: go test ./...

backend/internal/server/middleware/cors.go

@@ -1,24 +1,103 @@
 package middleware
 
 import (
+	"log"
+	"net/http"
+	"strings"
+	"sync"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
 	"github.com/gin-gonic/gin"
 )
 
+var corsWarningOnce sync.Once
+
 // CORS 跨域中间件
-func CORS() gin.HandlerFunc {
+func CORS(cfg config.CORSConfig) gin.HandlerFunc {
+	allowedOrigins := normalizeOrigins(cfg.AllowedOrigins)
+	allowAll := false
+	for _, origin := range allowedOrigins {
+		if origin == "*" {
+			allowAll = true
+			break
+		}
+	}
+	wildcardWithSpecific := allowAll && len(allowedOrigins) > 1
+	if wildcardWithSpecific {
+		allowedOrigins = []string{"*"}
+	}
+	allowCredentials := cfg.AllowCredentials
+
+	corsWarningOnce.Do(func() {
+		if len(allowedOrigins) == 0 {
+			log.Println("Warning: CORS allowed_origins not configured; cross-origin requests will be rejected.")
+		}
+		if wildcardWithSpecific {
+			log.Println("Warning: CORS allowed_origins includes '*'; wildcard will take precedence over explicit origins.")
+		}
+		if allowAll && allowCredentials {
+			log.Println("Warning: CORS allowed_origins set to '*', disabling allow_credentials.")
+		}
+	})
+	if allowAll && allowCredentials {
+		allowCredentials = false
+	}
+
+	allowedSet := make(map[string]struct{}, len(allowedOrigins))
+	for _, origin := range allowedOrigins {
+		if origin == "" || origin == "*" {
+			continue
+		}
+		allowedSet[origin] = struct{}{}
+	}
+
 	return func(c *gin.Context) {
-		// 设置允许跨域的响应头
-		c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
-		c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
+		origin := strings.TrimSpace(c.GetHeader("Origin"))
+		originAllowed := allowAll
+		if origin != "" && !allowAll {
+			_, originAllowed = allowedSet[origin]
+		}
+
+		if originAllowed {
+			if allowAll {
+				c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
+			} else if origin != "" {
+				c.Writer.Header().Set("Access-Control-Allow-Origin", origin)
+				c.Writer.Header().Add("Vary", "Origin")
+			}
+			if allowCredentials {
+				c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
+			}
+		}
+
 		c.Writer.Header().Set("Access-Control-Allow-Headers", "Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization, accept, origin, Cache-Control, X-Requested-With, X-API-Key")
 		c.Writer.Header().Set("Access-Control-Allow-Methods", "POST, OPTIONS, GET, PUT, DELETE, PATCH")
 
 		// 处理预检请求
-		if c.Request.Method == "OPTIONS" {
-			c.AbortWithStatus(204)
+		if c.Request.Method == http.MethodOptions {
+			if originAllowed {
+				c.AbortWithStatus(http.StatusNoContent)
+			} else {
+				c.AbortWithStatus(http.StatusForbidden)
+			}
 			return
 		}
 
 		c.Next()
 	}
 }
+
+func normalizeOrigins(values []string) []string {
+	if len(values) == 0 {
+		return nil
+	}
+	normalized := make([]string, 0, len(values))
+	for _, value := range values {
+		trimmed := strings.TrimSpace(value)
+		if trimmed == "" {
+			continue
+		}
+		normalized = append(normalized, trimmed)
+	}
+	return normalized
+}