go - oauth2 cannot fetch token: bad request
<p>I write a callback handler to login with Google account:</p>

<pre><code>func GoogleCallbackHandler(w http.ResponseWriter, r *http.Request) {
    conf:=&amp;oauth2.Config{
        ClientID:"700740834863-m4om9r91htn19htq2b6a05fu6vu4j7i5.apps.googleusercontent.com",
        ClientSecret:"...-rB",
        RedirectURL:"http://localhost:3000/auth/google/callback",
        Scopes:[]string{"profile"},
        Endpoint:google.Endpoint,
    }

    fmt.Println(conf.AuthCodeURL("state"))

    code := r.URL.Query().Get("code")

    token, err := conf.Exchange(oauth2.NoContext, code)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }

    client := conf.Client(oauth2.NoContext, token)
    resp, err := client.Get("https://www.googleapis.com/userinfo/v2/me")
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }

    raw, err := ioutil.ReadAll(resp.Body)
    defer resp.Body.Close()
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }

    var profile map[string]interface{}
    if err := json.Unmarshal(raw, &amp;profile); err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }

    session, _ := util.GlobalSessions.SessionStart(w, r)
    defer session.SessionRelease(w)

    session.Set("id_token", token.Extra("id_token"))
    session.Set("access_token", token.AccessToken)
    session.Set("profile", profile)

    // // Redirect to logged in page

    http.Redirect(w, r, "/user", http.StatusMovedPermanently)
}
</code></pre>

<p>In <code>main</code>, I serve handlers</p>

<pre><code>http.HandleFunc("/",route.IndexHandler)
http.HandleFunc("/auth/google/",route.GoogleCallbackHandler)
http.Handle("/user",negroni.New(
    negroni.HandlerFunc(route.IsAuthenticated),
    negroni.Wrap(http.HandlerFunc(route.UserHandler)),
))
</code></pre>

<p>I encounter the same problem I got with my old question:
<a href="https://stackoverflow.com/questions/35860811/oauth2-cannot-fetch-token-bad-request/">oauth2 cannot fetch token: bad request</a></p>

<pre><code>oauth2: cannot fetch token: 400 Bad Request
Response: {
  "error" : "invalid_request",
  "error_description" : "Missing required parameter: code"
}
</code></pre>

<p>After I asked this question last time, I managed to fix it with my above code, accessing and getting data successfully, but last night it suddenly got this error again, and I don't get why it no longer works after last few days working with totally same code</p>

<p>How can I get the <code>code</code> from <code>AuthCodeURL</code>? Is there any way to get the code for exchanging without redirecting to any other handler? I want to handle all things in just one this handler</p>