使用Gmail API快速入门进行多次授权

I was using Gmail's Quickstart application to extract the labels from an email account, but I hoped that there was a way to change to code so that a login page would always show up. There's a one-time authorization, but I wanted to know if there was a way to prompt authorization every time I start the app. The code that I've been using can be found right here: https://developers.google.com/gmail/api/quickstart/go

I will also attach the code below. Any help would be appreciated.

package main

import (
        "encoding/json"
        "fmt"
        "io/ioutil"
        "log"
        "net/http"
        "os"

        "golang.org/x/net/context"
        "golang.org/x/oauth2"
        "golang.org/x/oauth2/google"
        "google.golang.org/api/gmail/v1"
)

// Retrieve a token, saves the token, then returns the generated client.
func getClient(config *oauth2.Config) *http.Client {
        // The file token.json stores the user's access and refresh tokens, and is
        // created automatically when the authorization flow completes for the first
        // time.
        tokFile := "token.json"
        tok, err := tokenFromFile(tokFile)
        if err != nil {
                tok = getTokenFromWeb(config)
                saveToken(tokFile, tok)
        }
        return config.Client(context.Background(), tok)
}

// Request a token from the web, then returns the retrieved token.
func getTokenFromWeb(config *oauth2.Config) *oauth2.Token {
        authURL := config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
        fmt.Printf("Go to the following link in your browser then type the "+
                "authorization code: 
%v
", authURL)

        var authCode string
        if _, err := fmt.Scan(&authCode); err != nil {
                log.Fatalf("Unable to read authorization code: %v", err)
        }

        tok, err := config.Exchange(context.TODO(), authCode)
        if err != nil {
                log.Fatalf("Unable to retrieve token from web: %v", err)
        }
        return tok
}

// Retrieves a token from a local file.
func tokenFromFile(file string) (*oauth2.Token, error) {
        f, err := os.Open(file)
        if err != nil {
                return nil, err
        }
        defer f.Close()
        tok := &oauth2.Token{}
        err = json.NewDecoder(f).Decode(tok)
        return tok, err
}

// Saves a token to a file path.
func saveToken(path string, token *oauth2.Token) {
        fmt.Printf("Saving credential file to: %s
", path)
        f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
        if err != nil {
                log.Fatalf("Unable to cache oauth token: %v", err)
        }
        defer f.Close()
        json.NewEncoder(f).Encode(token)
}

func main() {
        b, err := ioutil.ReadFile("credentials.json")
        if err != nil {
                log.Fatalf("Unable to read client secret file: %v", err)
        }

        // If modifying these scopes, delete your previously saved token.json.
        config, err := google.ConfigFromJSON(b, gmail.GmailReadonlyScope)
        if err != nil {
                log.Fatalf("Unable to parse client secret file to config: %v", err)
        }
        client := getClient(config)

        srv, err := gmail.New(client)
        if err != nil {
                log.Fatalf("Unable to retrieve Gmail client: %v", err)
        }

        user := "me"
        r, err := srv.Users.Labels.List(user).Do()
        if err != nil {
                log.Fatalf("Unable to retrieve labels: %v", err)
        }
        if len(r.Labels) == 0 {
                fmt.Println("No labels found.")
                return
        }
        fmt.Println("Labels:")
        for _, l := range r.Labels {
                fmt.Printf("- %s
", l.Name)
        }
}

Got locked out of my account, so here's what I did.

First, on the main method, I added:

if exists("token.json") {
    os.Remove("token.json")
}

Then, I made that method:

func exists(filename string) bool {
    info, err := os.Stat(filename)
    if os.IsNotExist(err) {
        return false
    }
    return !info.IsDir()
}