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Authorizing with Google for REST APIs

When you want your Android app to access Google APIs using the user's Google account over HTTP, the GoogleAuthUtil class and related APIs provide your users a secure and consistent experience for picking an account and retrieving an OAuth 2.0 token for your app.

You can then use that token in your HTTP-based communications with Google API services that are not included in the Google Play services library, such as the Blogger or Translate APIs.

To get started with GoogleAuthUtil for accessing Google's REST APIs, you must set up your Android app project with the Google Play services library. Follow the procedures in Setup Google Play Services SDK.

Register your app

Before you can publish an app that retrieves an OAuth 2.0 token for Google REST APIs, you must register your Android app with the Google Cloud Console by providing your app's package name and the SHA1 fingerprint of the keystore with which you sign your release APK.

To register your Android app with Google Cloud Console:

  1. Visit Google Cloud Console.
  2. If you have an existing project to which you're adding an Android app, select the project. Otherwise, click Create project at the top, enter your project name and ID, then click Create. Note: The name you provide for the project is the name that appears to users in the Google Settings app in the list of Connected apps.

  3. In the left-side navigation, select APIs & auth.

  4. Enable the API you'd like to use by setting the Status to ON.
  5. In the left-side navigation, select Credentials.
  6. Click Create new client ID or Create new key as appropriate for your app.
  7. Complete the form that appears by filling in your Android app details. To get the SHA1 fingerprint for your app, run the following command in a terminal:

    keytool -exportcert -alias  -keystore  -list -v
    

    For example, you're using a debug-key with Eclipse, then the command looks like this:

    keytool -exportcert -alias androiddebugkey -keystore ~/.android/debug.keystore -list -v
    

    Then the keystore password is "android".

  8. Click Create.

The Credentials page then provides the available credentials such as an OAuth 2.0 client ID and an Android Key, but you don't need these to authorize your Android users. Simply registering your app with the package name and SHA1 makes the Google services accessible by your app.

To acquire the OAuth 2.0 token that will grant you access to Google APIs over HTTP, you need to first identify the user's Google account with which you'll query the servers. For this task, the Google Play services library provides a convenient account picker dialog you can invoke using AccountPicker. The result delivered to your activity from the account picker is the account name you'll use to request the OAuth 2.0 token in the next section.

Note: In order to use the APIs discussed here, you must include the Google Play services library with your project. If you haven't set up your project with the library yet, read the guide to Setup Google Play Services SDK.

Invoke the Account Picker

To open the account picker dialog that's managed by the Google Play services library, call startActivityForResult() using an Intent returned by AccountPicker.newChooseAccountIntent.

For example:

static final int REQUEST_CODE_PICK_ACCOUNT = 1000;

private void pickUserAccount() {
    String[] accountTypes = new String[]{"com.google"};
    Intent intent = AccountPicker.newChooseAccountIntent(null, null,
            accountTypes, false, null, null, null, null);
    startActivityForResult(intent, REQUEST_CODE_PICK_ACCOUNT);
}

When this code executes, a dialog appears for the user to pick an account. When the user selects the account, your activity receives the result in the onActivityResult() callback.

Most apps should pass the newChooseAccountIntent() method the same arguments shown in the above example, which indicate that:

  • There is no currently selected account.
  • There is no restricted list of accounts.
  • The dialog should list only accounts from the "com.google" domain.
  • Don't prompt the user to pick an account if there's only one available account (just use that one). However, even if only one account currently exists, the dialog may include an option for the user to add a new account.
  • There is no custom title for the dialog.
  • There is no specific auth token type required.
  • There are no restrictions based on account features.
  • There are no authenticator-specific options.

For more details about these arguments, see the newChooseAccountIntent() method.

Retrieve the Account Name

Once the user selects an account, your activity receives a call to its onActivityResult() method. The received Intent includes an extra for KEY_ACCOUNT_NAME, specifying the account name (an email address) you must use to acquire the OAuth 2.0 token.

Here's an example implementation of the callback onActivityResult() that receives the selected account:

String mEmail; // Received from newChooseAccountIntent(); passed to getToken()

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == REQUEST_CODE_PICK_ACCOUNT) {
        // Receiving a result from the AccountPicker
        if (resultCode == RESULT_OK) {
            mEmail = data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME);
            // With the account name acquired, go get the auth token
            getUsername();
        } else if (resultCode == RESULT_CANCELED) {
            // The account picker dialog closed without selecting an account.
            // Notify users that they must pick an account to proceed.
            Toast.makeText(this, R.string.pick_account, Toast.LENGTH_SHORT).show();
        }
    }
    // Handle the result from exceptions
    ...
}

You can now pass the account name held by mEmail to GoogleAuthUtil.getToken() (which is what the getUsername() method does), but because it performs network transactions, this method should not be called from the UI thread. The next lesson shows how to create an AsyncTask to get the auth token on a separate thread.

Once you have retrieved the account name for the user's Google account, you can call GoogleAuthUtil.getToken(), which returns the access token string required by Google API services.

Calling this method is generally a straightforward procedure, but you must be aware that:

This lesson shows how you can gracefully handle these concerns by performing authentication in an AsyncTask and providing users with the appropriate information and available actions during known exceptions.

Note: The code shown in this lesson, using GoogleAuthUtil.getToken(), is appropriate when you will be requesting the OAuth token from an Activity. However, if you need to request the OAuth token from a Service, then you should instead use getTokenWithNotification(). This method works the same as GoogleAuthUtil.getToken(), but if an error occurs, it also creates an appropriate notification that allows the user can recover from the error. The sample available for download above includes code showing how to use this method instead.

Extend AsyncTask to Get the Auth Token

The AsyncTask class provides a simple way to create a worker thread for jobs that should not run on your UI thread. This lesson focuses on how to create such a thread to get your auth token; for a more complete discussion about AsyncTask, read Keeping Your App Responsive and the AsyncTask class reference.

The doInBackground() method in your AsyncTask class is where you should call the GoogleAuthUtil.getToken() method. You can also use it to catch some of the generic exceptions that may occur during your network transactions.

For example, here's part of an AsyncTask subclass that calls GoogleAuthUtil.getToken():

public class GetUsernameTask extends AsyncTask{
    Activity mActivity;
    String mScope;
    String mEmail;

    GetUsernameTask(Activity activity, String name, String scope) {
        this.mActivity = activity;
        this.mScope = scope;
        this.mEmail = name;
    }

    /**
     * Executes the asynchronous job. This runs when you call execute()
     * on the AsyncTask instance.
     */
    @Override
    protected Void doInBackground(Void... params) {
        try {
            String token = fetchToken();
            if (token != null) {
                // **Insert the good stuff here.**
                // Use the token to access the user's Google data.
                ...
            }
        } catch (IOException e) {
            // The fetchToken() method handles Google-specific exceptions,
            // so this indicates something went wrong at a higher level.
            // TIP: Check for network connectivity before starting the AsyncTask.
            ...
        }
        return null;
    }

    /**
     * Gets an authentication token from Google and handles any
     * GoogleAuthException that may occur.
     */
    protected String fetchToken() throws IOException {
        try {
            **return GoogleAuthUtil.getToken(mActivity, mEmail, mScope);**
        } catch (UserRecoverableAuthException userRecoverableException) {
            // GooglePlayServices.apk is either old, disabled, or not present
            // so we need to show the user some UI in the activity to recover.
            mActivity.handleException(userRecoverableException);
        } catch (GoogleAuthException fatalException) {
            // Some other type of unrecoverable exception has occurred.
            // Report and log the error as appropriate for your app.
            ...
        }
        return null;
    }
    ...
}

In order to call GoogleAuthUtil.getToken(), you must provide the app Context, the account name retrieved from the account picker, and the scope for your auth token request. The above sample code (and the attached sample) defines these arguments with class members that the host activity passes to the AsyncTask class constructor. For more information about setting the scope, see the Specifying Scopes section below.

Once you have an AsyncTask subclass defined, you can instantiate and execute an instance after you get the user's account name from the account picker. For example, back in the Activity class you can do something like this:

String mEmail; // Received from newChooseAccountIntent(); passed to getToken()
        "oauth2:https://www.googleapis.com/auth/userinfo.profile";

/**
 * Attempts to retrieve the username.
 * If the account is not yet known, invoke the picker. Once the account is known,
 * start an instance of the AsyncTask to get the auth token and do work with it.
 */
private void getUsername() {
    if (mEmail == null) {
        pickUserAccount();
    } else {
        if (isDeviceOnline()) {
            **new GetUsernameTask(HelloActivity.this, mEmail, SCOPE).execute();**
        } else {
            Toast.makeText(this, R.string.not_online, Toast.LENGTH_LONG).show();
        }
    }
}

For information about how to check whether the device is currently online (as performed by the isDeviceOnline() method above), see the attached sample app or the Connecting to the Network lesson.

The only part left is how you should handle the exceptions that may occur when you call GoogleAuthUtil.getToken().

Specifying scopes

The scope string is used to specify which Google services can be accessed by an app using the requested auth token. An auth token can be associated with multiple scopes.

When specifying the scopes in your auth token request, prefix the scope string with "oauth2:" followed by a list of one or more OAuth scope values. Use a space to separate each scope value in the list. To see a list of valid OAuth scope values for Google services, browse the OAuth 2.0 Playground.

Tip: Specify "oauth2:<scope>" for a single scope. Specify "oauth2:<scope1> <scope2> <scopeN>" for multiple scopes (using a space to separate each scope).

For example, to access the Google Books API, the scope is "oauth2:https://www.googleapis.com/auth/books". To add an additional scope, say for Google+ login, your code might look like this:

private final static String BOOKS_API_SCOPE
        = "https://www.googleapis.com/auth/books";
private fina; static String GPLUS_SCOPE
        = "https://www.googleapis.com/auth/plus.login";
private final static String mScopes
        = "oauth2:" + BOOKS_API_SCOPE + " " + GPLUS_SCOPE;
String token = GoogleAuthUtil.getToken(mActivity, mEmail, mScopes);

Handle Exceptions

As shown in the fetchToken() method above, you must catch all occurrences of GoogleAuthException when you call GoogleAuthUtil.getToken().

To provide users information and a proper solution to issues that may occur while acquiring the auth token, it's important that you properly handle the following subclasses of GoogleAuthException:

For example, the fetchToken() method in the above sample code catches any occurrence of UserRecoverableAuthException and passes it back to the activity with a method called handleException(). Here's what that method in the activity may look like:

static final int REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR = 1001;

/**
 * This method is a hook for background threads and async tasks that need to
 * provide the user a response UI when an exception occurs.
 */
public void handleException(final Exception e) {
    // Because this call comes from the AsyncTask, we must ensure that the following
    // code instead executes on the UI thread.
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            if (e instanceof GooglePlayServicesAvailabilityException) {
                // The Google Play services APK is old, disabled, or not present.
                // Show a dialog created by Google Play services that allows
                // the user to update the APK
                int statusCode = ((GooglePlayServicesAvailabilityException)e)
                        .getConnectionStatusCode();
                Dialog dialog = GooglePlayServicesUtil.getErrorDialog(statusCode,
                        HelloActivity.this,
                        REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR);
                dialog.show();
            } else if (e instanceof UserRecoverableAuthException) {
                // Unable to authenticate, such as when the user has not yet granted
                // the app access to the account, but the user can fix this.
                // Forward the user to an activity in Google Play services.
                Intent intent = ((UserRecoverableAuthException)e).getIntent();
                startActivityForResult(intent,
                        REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR);
            }
        }
    });
}

Notice that in both cases, the REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR request code is passed with the request to handle the exception with a dialog or activity. This way, when the user completes the appropriate action to resolve the exception, your onActivityResult() method receives an intent that includes this request code and you can try to acquire the auth token again.

For example, the following code is a complete implementation of onActivityResult() that handles results for both the REQUEST_CODE_PICK_ACCOUNT action and the REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR action, which occurs after the user completes one of the actions above to resolve an exception.

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == REQUEST_CODE_PICK_ACCOUNT) {
        // Receiving a result from the AccountPicker
        if (resultCode == RESULT_OK) {
            mEmail = data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME);
            // With the account name acquired, go get the auth token
            getUsername();
        } else if (resultCode == RESULT_CANCELED) {
            // The account picker dialog closed without selecting an account.
            // Notify users that they must pick an account to proceed.
            Toast.makeText(this, R.string.pick_account, Toast.LENGTH_SHORT).show();
        }
    } else if ((requestCode == REQUEST_CODE_RECOVER_FROM_AUTH_ERROR ||
            requestCode == REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR)
            && resultCode == RESULT_OK) {
        // Receiving a result that follows a GoogleAuthException, try auth again
        getUsername();
    }
}