Go で HTTP POST リクエストと Cookie を効果的に管理するにはどうすればよいですか?

import (
    "net/http"
    "net/http/cookiejar"
    "net/url"
)

func Login(user, password string) {
    postUrl := "http://www.example.com/login"

    // Set up login form data
    values := make(url.Values)
    values.Set("user", user)
    values.Set("password", password)

    // Create a cookie jar for storing cookies
    jar, err := cookiejar.New(nil)
    if err != nil {
        // Handle error
    }

    // Create an HTTP client with the cookie jar
    client := &http.Client{
        Jar: jar,
    }

    // Submit the form using the client
    resp, err := client.PostForm(postUrl, values)
    if err != nil {
        // Handle error
    }
    defer resp.Body.Close()

    // Cookies are now stored in the cookie jar
}

func ViewBill(url string) {
    // Assuming the client with the cookie jar is already created
    resp, err := client.Get(url)
    if err != nil {
        // Handle error
    }
    defer resp.Body.Close()

    // The stored cookies will be used automatically for this request
}