fix duplicated cors headers

cors.go

@@ -4,10 +4,19 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
+// this function is aborded
 func corsMiddleware() gin.HandlerFunc {
 	return func(c *gin.Context) {
-		c.Header("Access-Control-Allow-Origin", "*")
-		c.Header("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE, PATCH")
-		c.Header("Access-Control-Allow-Headers", "Origin, Authorization, Content-Type")
+		// set cors header
+		header := c.Request.Header
+		if header.Get("Access-Control-Allow-Origin") == "" {
+			c.Header("Access-Control-Allow-Origin", "*")
+		}
+		if header.Get("Access-Control-Allow-Methods") == "" {
+			c.Header("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE, PATCH")
+		}
+		if header.Get("Access-Control-Allow-Headers") == "" {
+			c.Header("Access-Control-Allow-Headers", "Origin, Authorization, Content-Type")
+		}
 	}
 }