Membuat middleware auth pada gin

package auth

import (
    "fmt"
    "net/http"
    "strings"

    "github.com/dgrijalva/jwt-go"
    "github.com/gin-gonic/gin"
)

type header struct {
    Authorization string `header:"Authorization"`
}

func Auth() gin.HandlerFunc {
    return func(c *gin.Context) {
        h := header{}

        if err := c.ShouldBindHeader(&h); err != nil {
            c.JSON(http.StatusInternalServerError, gin.H{
                "status": "failed",
            })
            return
        }

        if h.Authorization == "" {
            c.JSON(http.StatusBadRequest, gin.H{
                "message": "Access is denied",
            })
            return
        }

        tokenString := strings.ReplaceAll(h.Authorization, "Bearer ", "")
        token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
            // Don't forget to validate the alg is what you expect:
            if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
                return nil, fmt.Errorf("Unexpected signing method: %v", token.Header["alg"])
            }

            // hmacSampleSecret is a []byte containing your secret, e.g. []byte("my_secret_key")
            hmacSampleSecret := []byte("my_secret_key")
            return hmacSampleSecret, nil
        })
        if err != nil {
            c.JSON(http.StatusInternalServerError, gin.H{
                "message": "InternalServerError",
            })
            return
        }

        claims, ok := token.Claims.(jwt.MapClaims)
        if !ok {
            c.JSON(http.StatusInternalServerError, gin.H{
                "message": "InternalServerError",
            })
            return
        }

        // c.Set("userId", claims["foo"])
        id, _ := claims["id"].(float64)
        c.Set("userId", int(id))

        c.Next()

        // claims["foo"]
    }
}