token.go

/**
 * Copyright (c) Google Developers Site
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// This file copied from https://developers.google.com/drive/api/v3/quickstart/go and modified.

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"os"

	"github.com/kelseyhightower/envconfig"
	"golang.org/x/oauth2"
	"google.golang.org/api/drive/v3"
)

func getOAuth2Config() (*oauth2.Config, error) {
	config := struct {
		GoogleClientID     string `envconfig:"GOOGLE_CLIENT_ID",required:"true"`
		GoogleClientSecret string `envconfig:"GOOGLE_CLIENT_SECRET",required:"true"`
	}{}
	if err := envconfig.Process("DT", &config); err != nil {
		return nil, err
	}
	return &oauth2.Config{
		ClientID:     config.GoogleClientID,
		ClientSecret: config.GoogleClientSecret,
		RedirectURL:  "urn:ietf:wg:oauth:2.0:oob",
		Scopes:       []string{drive.DriveScope},
		Endpoint: oauth2.Endpoint{
			AuthURL:  "https://accounts.google.com/o/oauth2/auth",
			TokenURL: "https://oauth2.googleapis.com/token",
		},
	}, nil
}

func getTokenFromWeb(config *oauth2.Config) (*oauth2.Token, error) {
	authURL := config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
	fmt.Printf("Go to the following link in your browser then type the "+
		"authorization code: \n%v\n", authURL)

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

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

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
}

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

func getClient(config *oauth2.Config) (*http.Client, error) {
	tokFile := "token.json"
	tok, err := tokenFromFile(tokFile)
	if err != nil {
		tok, err := getTokenFromWeb(config)
		if err != nil {
			return nil, err
		}
		if err := saveToken(tokFile, tok); err != nil {
			return nil, err
		}
	}
	return config.Client(context.Background(), tok), nil
}