Using Google Oauth2 to Access Google User Data from Client Application

using System;
using System.Threading;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Oauth2.v2;
using Google.Apis.Auth.OAuth2.Responses;
using Google.Apis.Oauth2.v2.Data;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using Google.GData.Client;
using Google.GData.Extensions;
using Google.GData.Contacts;
using Google.Contacts;
namespace EmailClient
{

public class GmailLogin {
private static string xoauthKey;
private static string userEmail;
private static string userName;
private static UserCredential credential;
private static string[] contacts;
private static string[,]contactDetails;
private static int totContacts;
private static ContactsRequest cr;
private static readonly GmailLogin
m_Instance =new

GmailLogin();

// Prevent instance creation from other classes using singleton design pattern
private GmailLogin() {
}

public static GmailLogin Instance

{
get {
return m_Instance;
}
}

public bool GoogleLogin() {
// Request Gmail IMAP/SMTP scope and the e-mail address scope.
string[] scopes = new string[]{ “https:
//mail.google.com/”, Oauth2Service.Scope.UserinfoEmail, Oauth2Service.Scope.UserinfoProfile, “https://www.google.com/m8/feeds/" };
Console.WriteLine(“Requesting authorization”);
credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
new ClientSecrets
{
ClientId = “specify your client_ID here”,
ClientSecret = “specify your client_secret here”,
},
scopes,
“user”,
CancellationToken.None).Result;
Console.WriteLine(“Authorization granted or not required( if the saved access token
already available)”);
/*
*
* access token is also saved locally in a persistent location
* C:\Users\UserName\AppData\Roaming\Google.Apis.Auth\Google.Apis.Auth.OAuth2.Responses.TokenResponse-user
* for later use.
*/
if (credential.Token.IsExpired(credential.Flow.Clock)) {
Console.WriteLine(“The access token has expired, refreshing it”);
try {
if (credential.RefreshTokenAsync(CancellationToken.None).Result) {
Console.WriteLine(“The access token is now refreshed”);
return true;
} else {
Console.WriteLine(“The access token has expired but we can’t refresh it”);
return false;
}
} catch (Exception ex) {
Console.WriteLine(ex.Message);
return false;
}
} else {
Console.WriteLine(“The access token is OK, continue”);
return true;
}
}

public void RequestEmail() {
Console.WriteLine(“Requesting the e - mail address of the user from Google”);

Oauth2Service oauthService = new Oauth2Service(
new BaseClientService.Initializer() {
HttpClientInitializer =GmailLogin.getCredential()
});
Userinfoplus userInfo = oauthService.Userinfo.Get().ExecuteAsync().Result;
userEmail = userInfo.Email;
userName = userInfo.Name;
Console.WriteLine(“E - mail address is “ + userEmail);
//to access user’s contact list
RequestSettings settings = new RequestSettings(“Google Sync.”, GmailLogin.getCredential().Token.AccessToken) {
AutoPaging =true,
UseSSL =true
};
cr = new ContactsRequest(settings);
FetchAllContacts(cr, userEmail);


// Build XOAUTH2 token to use Gmail IMAP or SMTP.
xoauthKey = OAuth2.GetXOAuthKeyStatic(userEmail, GmailLogin.getCredential().Token.AccessToken);
// return true;
}

public void RevokeAccessToken() {
FileDataStore ds = new FileDataStore(GoogleWebAuthorizationBroker.Folder);
ds.DeleteAsync<TokenResponse> (“user”).Wait();
}

public static string getUserEmail() {
return userEmail;
}

public void FetchAllContacts(ContactsRequest cr, String email) {
Feed<Contact> feed = cr.GetContacts(email);
int i = 0;
Console.WriteLine(feed.TotalResults);
contacts = new string[feed.TotalResults];
contactDetails = new string[feed.TotalResults, 3];
totContacts = feed.TotalResults;
foreach(Contact entry in feed.Entries)
{
//Console.WriteLine(entry.Name.FullName);
//entry.Id
contactDetails[i, 0] =entry.Id;
contactDetails[i, 1] =entry.Name.FullName;

foreach(EMail e in entry.Emails)
{
Console.WriteLine(“\t” + e.Address);
contacts[i] = e.Address;
// Console.WriteLine(contacts[i]);
contactDetails[i, 2] =e.Address;
i++;
}
}
}

public static string[] getContacts() {
return contacts;
}

public static string[,]

getContactDetails() {
return contactDetails;
}

public static string getUserName() {
return userName;
}

public static string getOauthKey() {
return xoauthKey;
}

public static int getTotContacts() {
return totContacts;
}

public static bool DeleteContact(Uri contactURL) {
// Retrieving the contact is required in order to get the Etag.
Contact contact = cr.Retrieve < Contact > (contactURL);
try {
cr.Delete(contact);
return true;
} catch (GDataVersionConflictException e) {
Console.WriteLine(e.Message);
return false;
}
}

public static UserCredential getCredential() {
return credential;
}
}
}

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Software Engineer | GSoC Intern | CSE Graduate

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Sathya Bandara

Sathya Bandara

Software Engineer | GSoC Intern | CSE Graduate

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