It appears Google is making some concessions for developers who are not keen on forcing their users to have a Google+ account to use their apps.
Google+ Sign-In now supports all Google account types, including Google Apps users and those without a Google+ profile. This seems incongruent with recent updates to Google services that force users to have a Google+ profile on the company’s so-called social network in order to interact with the service. When YouTube restricted video comments to only those with Google+ accounts, the community was not happy.
Though it appears Google is making some effort to appease developers, especially those building enterprise applications that would not previously support Google+ login. According to the company, it will be easy to upgrade from Open ID v2 or OAuth 2.0 Login.
Google+ Sign-In also supports over-the-air installs, interactive posts that let users share posts or messages to promote the app or service, and cross-device sign-in. It is fully compatible with the OpenID standard.
In addition to a broader login update, Google is also introducing incremental auth, a less-invasive way of asking users to accept app permissions. For example, if your app allows users to save pictures to Google Drive, you can ask for only basic information when a consumer downloads the application and request photo-access permissions when they are ready to start saving and sharing images.
Incremental auth will be especially helpful for deterring users that hesitate giving up broader permissions up front. The company recommends developers only ask for basic permissions at first to "reduce friction and increase app engagement."