Posted by William Denniss, Product Manager, Identity and Authentication
Support for ClientLogin, OAuth 1.0 (3LO1), AuthSub, and OpenID 2.0 has ended, and the shutdown process has begun. Clients attempting to use these services will begin to fail and must be migrated to OAuth 2.0 or OpenID Connect immediately.
To migrate a sign-in system, the easiest path is to use the Google Sign-in SDKs (see the migration documentation). Google Sign-in is built on top of our standards-based OAuth 2.0 and OpenID Connect infrastructure and provides a single interface for authentication and authorization flows on Web, Android and iOS. To migrate server API use, we recommend using one of our OAuth 2.0 client libraries.
We are moving away from legacy authentication protocols, focusing our support on OpenID Connect and OAuth 2.0. These modern open standards enhance the security of Google accounts, and are generally easier for developers to integrate with.
13LO stands for 3-legged OAuth where there's an end-user that provides consent. In contrast, 2-legged (2LO) correspond to Enterprise authorization scenarios such as organizational-wide policies control access. Both OAuth1 3LO and 2LO flows are deprecated, but this announcement is specific to OAuth1 3LO.