func main() {
    auth, err := jwt.New(jwt.Auth{
        SecretKey: []byte("must change here"),

        // Authenticator authenticates a request and return jwt.MapClaims
        // that contains a user information of the request.
        Authenticator: func(c *gin.Context) (jwt.MapClaims, error) {
            var loginForm LoginForm
            if err := c.ShouldBind(&loginForm); err != nil {
                return nil, jwt.ErrorAuthenticationFailed
            }

            u, ok := authenticate(req.Username, req.Password)
            if ok {
                return nil, jwt.ErrorAuthenticationFailed
            }

            return jwt.MapClaims{
                "username": u.Username,
                "role":     u.Role,
            }, nil
        },

        // UserFetcher takes a jwt.MapClaims and return a user object.
        UserFetcher: func(c *gin.Context, claims jwt.MapClaims) (interface{}, error) {
            username, ok := claims["username"].(string)
            if !ok {
                return nil, nil
            }
            return findByUsername(username)
        },
    })

    // some lines

    e.Use(jwt.ErrorHandler)

    // issue authorization token
    e.POST("/login", auth.AuthenticateHandler)

    // refresh token expiration
    e.POST("/auth/refresh_token", auth.RefreshHandler)

    // role management
    e.GET("/operator/hello", Operator(auth), SayHello) // this is only for Operator
    e.GET("/admin/hello", Admin(auth), SayHello) // this is only for Admin
}