main.go

package main
import (
    "fmt"
	"github.com/gin-gonic/gin"
)

func CORSMiddleware() gin.HandlerFunc {
    return func(c *gin.Context) {

        c.Writer.Header().Set("Content-Type", "application/json")
        c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
        c.Writer.Header().Set("Access-Control-Allow-Headers", "Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization")
        if c.Req.Method == "OPTIONS" {
            fmt.Println("options")
            c.Abort(200)
            return
        }
        
        c.Next()
    }
}

func main() {
    r := gin.Default()
    r.Use(CORSMiddleware())
    r.GET("", func (g *gin.Context) {
        g.JSON(200, gin.H{"foo":"bar"})
    })

    r.Run(":8082")
}

response.txt

HTTP/1.1 200 OK
Access-Control-Allow-Headers: Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization
Access-Control-Allow-Origin: *
Content-Type: application/json
Date: Thu, 03 Jul 2014 11:33:38 GMT
Content-Length: 14