OAuth flow using the AccountManager on Android

AndroidManifest.xml

<!-- ... -->

<uses-permission android:name="android.permission.GET_ACCOUNTS" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.USE_CREDENTIALS" />

<!-- ... -->

AuthActivity.java

import android.accounts.Account;
import android.accounts.AccountManager;
import android.accounts.AccountManagerCallback;
import android.accounts.AccountManagerFuture;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class AuthActivity extends Activity {

  private static final int AUTHORIZATION_CODE = 1993;
	private static final int ACCOUNT_CODE = 1601;

	private AuthPreferences authPreferences;
	private AccountManager accountManager;

	/**
	 * change this depending on the scope needed for the things you do in
	 * doCoolAuthenticatedStuff()
	 */
	private final String SCOPE = "https://www.googleapis.com/auth/googletalk";

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);

		accountManager = AccountManager.get(this);

		authPreferences = new AuthPreferences(this);
		if (authPreferences.getUser() != null
				&& authPreferences.getToken() != null) {
			doCoolAuthenticatedStuff();
		} else {
			chooseAccount();
		}
	}

	private void doCoolAuthenticatedStuff() {
		// TODO: insert cool stuff with authPreferences.getToken()

		Log.e("AuthApp", authPreferences.getToken());
	}

	private void chooseAccount() {
		// use https://github.com/frakbot/Android-AccountChooser for
		// compatibility with older devices
		Intent intent = AccountManager.newChooseAccountIntent(null, null,
				new String[] { "com.google" }, false, null, null, null, null);
		startActivityForResult(intent, ACCOUNT_CODE);
	}

	private void requestToken() {
		Account userAccount = null;
		String user = authPreferences.getUser();
		for (Account account : accountManager.getAccountsByType("com.google")) {
			if (account.name.equals(user)) {
				userAccount = account;

				break;
			}
		}

		accountManager.getAuthToken(userAccount, "oauth2:" + SCOPE, null, this,
				new OnTokenAcquired(), null);
	}

	/**
	 * call this method if your token expired, or you want to request a new
	 * token for whatever reason. call requestToken() again afterwards in order
	 * to get a new token.
	 */
	private void invalidateToken() {
		AccountManager accountManager = AccountManager.get(this);
		accountManager.invalidateAuthToken("com.google",
				authPreferences.getToken());

		authPreferences.setToken(null);
	}

	@Override
	protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		super.onActivityResult(requestCode, resultCode, data);

		if (resultCode == RESULT_OK) {
			if (requestCode == AUTHORIZATION_CODE) {
				requestToken();
			} else if (requestCode == ACCOUNT_CODE) {
				String accountName = data
						.getStringExtra(AccountManager.KEY_ACCOUNT_NAME);
				authPreferences.setUser(accountName);

				// invalidate old tokens which might be cached. we want a fresh
				// one, which is guaranteed to work
				invalidateToken();

				requestToken();
			}
		}
	}

	private class OnTokenAcquired implements AccountManagerCallback<Bundle> {

		@Override
		public void run(AccountManagerFuture<Bundle> result) {
			try {
				Bundle bundle = result.getResult();

				Intent launch = (Intent) bundle.get(AccountManager.KEY_INTENT);
				if (launch != null) {
					startActivityForResult(launch, AUTHORIZATION_CODE);
				} else {
					String token = bundle
							.getString(AccountManager.KEY_AUTHTOKEN);

					authPreferences.setToken(token);

					doCoolAuthenticatedStuff();
				}
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
	}
}

AuthPreferences.java

import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;

public class AuthPreferences {

	private static final String KEY_USER = "user";
	private static final String KEY_TOKEN = "token";

	private SharedPreferences preferences;

	public AuthPreferences(Context context) {
		preferences = context
				.getSharedPreferences("auth", Context.MODE_PRIVATE);
	}

	public void setUser(String user) {
		Editor editor = preferences.edit();
		editor.putString(KEY_USER, user);
		editor.commit();
	}

	public void setToken(String password) {
		Editor editor = preferences.edit();
		editor.putString(KEY_TOKEN, password);
		editor.commit();
	}

	public String getUser() {
		return preferences.getString(KEY_USER, null);
	}

	public String getToken() {
		return preferences.getString(KEY_TOKEN, null);
	}
}

Thanks a lot! Helped me from a great trouble.

So I put the
if (authPreferences.getUser() != null && authPreferences.getToken() != null)

Inside a onClick and when I press Ok after selecting a gmail account, the app crashes. I am hoping to use this to do oAuth2 so any help would be greatly appreciated. The question can be found on StackOverflow here http://stackoverflow.com/questions/38968532/app-crashing-after-selecting-gmail-account-oauth2

Joy... I revoked permission of my email to this code and now the permission dialog doesn't show anymore...I now get a BinderProxy error

This gist helped me, thanks! I didn't know "oauth2:" is necessary at the beginning of scope.