Created
August 29, 2020 13:59
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Get email address of user logging in using Google OAuth 2
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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" | |
googoauth2 "google.golang.org/api/oauth2/v2" | |
) | |
// 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: \n%v\n", 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\n", 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() { | |
// Credentials obtained by creating a Google OAuth 2.0 Client ID using the Google APIs console. | |
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, googoauth2.UserinfoEmailScope) | |
if err != nil { | |
log.Fatalf("Unable to parse client secret file to config: %v", err) | |
} | |
client := getClient(config) | |
srv, err := googoauth2.New(client) | |
if err != nil { | |
log.Fatalf("Unable to create OAuth 2 Client: %v", err) | |
} | |
info, err := srv.Userinfo.V2.Me.Get().Do() | |
if err != nil { | |
log.Fatalf("Unable to get current user info: %v", err) | |
} | |
fmt.Println(info.Email) | |
} |
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