With Google Sign-In , developers would need to work with a new service called Google Identity. going away But As with Google, this has become a mess of docs and seemingly relevant code which will render your app unusable. My team spent two days implementing both of them due to this mess. So I am gonna make it simple for you to decide. With this Google Identity service, Google has designed two flows Sign-In flows - Apps that just need to know the user’s email and name for auth Authorization - Apps that need to access Docs API, Sheets API on behalf of the user. Sign-In flows This is the newest sign-in-flow for developers without much need for handling oauth. It goes like this, App code triggers a google-sign in your code gets back JWT token using a standard JWT decoder, you can read names and emails. It is that simple. Steps: Configure WebApp consent screen in GCP. Read https://developers.google.com/identity/gsi/web/guides/get-google-api-clientid Load Google Library - https://developers.google.com/identity/gsi/web/guides/client-library Display the Sign-In Button - https://developers.google.com/identity/gsi/web/guides/display-button Add A Server script/endpoint to handle the JWT token. Authorization If you are the developer building integration with Google APIs, forgot above and you must do Authorisation flow. I know names are confusing. But let it be. You need Auth from the user to access his/her google docs. So, Authorisation for you. Steps: Load the client library into your webpage - https://developers.google.com/identity/oauth2/web/guides/load-3p-authorization-library Trigger and Process the Google OAuth flow - It’s a typical OAuth2 Workflow most platforms offer like Github, Bitbucket, Facebook. . (See note below) https://developers.google.com/identity/oauth2/web/guides/use-code-model Note: There are two models of authorization: Code model and Token model. . https://developers.google.com/identity/oauth2/web/guides/choose-authorization-model Token model is useful only if all the actions are done from the user’s browser. If you want to use that, Refer . https://developers.google.com/identity/oauth2/web/guides/use-token-model If your apps work offline, Go with the Code model as shown in the above steps. This was an introductory article to give a general idea of Google Identity Services. It is not a step-by-step tutorial. Google Docs has provided all that but in a messy structure. So I have given you direct links. Enjoy!
