Android: using Google sign in to get access token

Question

After reading the last Google + news at here and this. How do I get access token after I complete the sign in?

Answer 1

To answer doubts about oauth scope (just to be useful for googlers):

To fully understand, Google-it some about authentication and authorization concepts.

Check if user/password exists is about authentication part.

Scope is required to authorization part: what you are authorized to do or receive in behalf of user. To get a list of scopes allowed, check the OAuth service documentation.

From Google and G+, most common scopes can be found on: https://developers.google.com/+/api/oauth?hl=pt-ZA

For example, to get all possible information from user, you can use the scope:

"openid profile email https://www.googleapis.com/auth/plus.login https://www.googleapis.com/auth/plus.me"

(the first word refer to protocol, followed by words that ask for fields on response, and desired scopes can be declared toghether with a space separator)

Note: Later, if you try use your access token to request or do anything that you don't asked before with a scope, the service can return an authorization error.

For Google, a good tool you can use to learn about his OAuth service and scope is the OAuth Playground: https://developers.google.com/oauthplayground/

Answer 2

Did you have a look at the API reference?

The class you are probably looking for is com.google.android.gms.auth.GoogleAuthUtil.

It provides, amongst others, the following method:
static String getToken(Context context, String accountName, String

Description:
Authenticates the user and returns a valid Google authentication token, or throws an exception if there was an error getting a token.

Usage:

String token;
try {
    token = GoogleAuthUtil.getToken(context, accountName, scope);
} catch (GooglePlayServicesAvailabilityException playEx) {
    Dialog dialog = GooglePlayServicesUtil.getErrorDialog(
        playEx.getConnectionStatusCode(),
        Activity.this,
        AUTH_REQUEST_CODE);
    // Use the dialog to present to the user.
} catch (UserRecoverableAutException recoverableException) {
    Intent recoveryIntent = recoverableException.getIntent();
    // Use the intent in a custom dialog or just startActivityForResult.
} catch (GoogleAuthException authEx) {
    // This is likely unrecoverable.
    Log.e(TAG, "Unrecoverable authentication exception: " + authEx.getMesssage(), authEx);
} catch (IOException ioEx) {
    Log.i(TAG, "transient error encountered: " + ioEx.getMessage());
    doExponentialBackoff();
}