$ go doc http.Client.Jar
struct Client {
    // Jar specifies the cookie jar.
    //
    // The Jar is used to insert relevant cookies into every
    // outbound Request and is updated with the cookie values
    // of every inbound Response. The Jar is consulted for every
    // redirect that the Client follows.
    //
    // If Jar is nil, cookies are only sent if they are explicitly
    // set on the Request.
    Jar CookieJar
}
$