go-twitter library - app authentication doesn't fetch user timelines

app-auth.go

package main

import (
    "fmt"
    "github.com/dghubble/go-twitter/twitter"
    "golang.org/x/oauth2"
    "os"
)

func main() {

    config := &oauth2.Config{}
    token := &oauth2.Token{AccessToken: os.Getenv("ACCESS_CODE")}
    // OAuth2 http.Client will automatically authorize Requests
    httpClient := config.Client(oauth2.NoContext, token)

    // Twitter client
    client := twitter.NewClient(httpClient)

    // user show
    userShowParams := &twitter.UserShowParams{ScreenName: "golang"}
    user, _, err := client.Users.Show(userShowParams)
    fmt.Printf("USERS SHOW:\n%+v\n", user)
    fmt.Printf("Error with Users show: %+v\n", err)

    // users lookup
    userLookupParams := &twitter.UserLookupParams{ScreenName: []string{"golang", "gophercon"}}
    users, _, err := client.Users.Lookup(userLookupParams)
    fmt.Printf("USERS LOOKUP:\n%+v\n", users)
    fmt.Printf("Error with users lookup: %+v\n", err)

    // status show
    statusShowParams := &twitter.StatusShowParams{}
    tweet, _, err := client.Statuses.Show(584077528026849280, statusShowParams)
    fmt.Printf("STATUSES SHOW:\n%+v\n", tweet)
    fmt.Printf("Error with status show: %+v\n", err)

    // statuses lookup
    statusLookupParams := &twitter.StatusLookupParams{ID: []int64{20}, TweetMode: "extended"}
    tweets, _, err := client.Statuses.Lookup([]int64{573893817000140800}, statusLookupParams)
    fmt.Printf("STATUSES LOOKUP:\n%+v\n", tweets)
    fmt.Printf("Error with status lookup %+v\n", err)

    // oEmbed status
    statusOembedParams := &twitter.StatusOEmbedParams{ID: 691076766878691329, MaxWidth: 500}
    oembed, _, err := client.Statuses.OEmbed(statusOembedParams)
    fmt.Printf("OEMBED TWEET:\n%+v\n", oembed)
    fmt.Printf("Error with Oembed tweet: %+v\n", err)

    // user timeline
    userTimelineParams := &twitter.UserTimelineParams{ScreenName: "_icyflame", Count: 2}
    tweets, _, err = client.Timelines.UserTimeline(userTimelineParams)
    fmt.Printf("USER TIMELINE:\n%+v\n", tweets)
    fmt.Printf("Error with User timeline: %+v\n", err)

    // search tweets
    searchTweetParams := &twitter.SearchTweetParams{
        Query:     "happy birthday",
        TweetMode: "extended",
        Count:     3,
    }
    search, _, err := client.Search.Tweets(searchTweetParams)
    fmt.Printf("SEARCH TWEETS:\n%+v\n", search)
    fmt.Printf("SEARCH METADATA:\n%+v\n", search.Metadata)
    fmt.Printf("Error with Search: %+v\n", err)

}