initial: ZeroTier-like P2P mesh VPN server with multi-tenant Web UI

internal/middleware/cors.go

@@ -0,0 +1,29 @@
+package middleware
+
+import (
+	"github.com/gin-gonic/gin"
+)
+
+func CORS(allowedOrigins []string) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		origin := c.GetHeader("Origin")
+		for _, allowed := range allowedOrigins {
+			if allowed == "*" || allowed == origin {
+				c.Header("Access-Control-Allow-Origin", origin)
+				break
+			}
+		}
+		if origin == "" {
+			c.Header("Access-Control-Allow-Origin", "*")
+		}
+		c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
+		c.Header("Access-Control-Allow-Headers", "Content-Type, Authorization")
+		c.Header("Access-Control-Allow-Credentials", "true")
+
+		if c.Request.Method == "OPTIONS" {
+			c.AbortWithStatus(204)
+			return
+		}
+		c.Next()
+	}
+}