golang cannot use middleware

I'm trying to implementing middleware for authorization.

main function :

func main() {

    http.HandleFunc("/register", handlers.Register)
    http.HandleFunc("/login", handlers.Login)
    http.HandleFunc("/ex", middleware.RequireAuth(handlers.Ex))

    http.ListenAndServe(":8080", nil)
}

middleware:

package middleware

import (
    "context"
    "net/http"

    jwt "github.com/movie/JWT"
)

func RequireAuth(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token, err := r.Cookie("authorization")
        if err != nil {
            http.Error(w, err.Error(), http.StatusNotFound)

            return
        }

        claims, err := jwt.ValidateToken(token.Value)
        if err != nil {
            http.Error(w, err.Error(), http.StatusNotAcceptable)

            return
        }

        ctx := context.WithValue(r.Context(), "username", claims["username"])
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

handler:

func Ex(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("hiihihihihi"))
}

This gives me an error.

cannot use middleware.RequireAuth(handlers.Ex) (value of type http.Handler) as func(http.ResponseWriter, *http.Request) value in argument to http.HandleFunc

How can I fix this?