 Hi, everyone. I'm Eiji. In a previous video, we've looked at authentication using Google Sign in. In this video, let's learn how to integrate with a backend. This will allow you to keep sessions and store user data in a database on the server. When authenticating with backends, you deal with something called ID token. It contains the issuer of this token, which app this is for, an expression date, and so on. You can verify the user's identity and its integrity by examining the ID token's content. Let's get started. You can obtain an ID token upon the successful authentication and then send it over to the server using a secure HTTPS connection. On the server side, the retrieved ID token will look pretty cryptic. But don't worry. You can decode, verify, and extract this information without a network call by using the Google-provided client libraries, like this. Note that the client libraries verify most of the information, but you still have to check if AUD, which indicates audience matches your client ID, and the ISS, which indicates issuer matches either of following strings. Now, you can retrieve the user's profile information to be used in your app. This ID token includes the same profile information you can get using the JavaScript library on the client. A quick tip to remember is that if the user's email address is already verified by Google, you don't have to verify it again in your app. Once the ID token is verified, use SUB, which indicates subject as a user ID to store information. Remember, don't use the email address as a primary key for users, as it might change in the future. OK, now you are ready to integrate Google Sign In with Backend. In the next video, I will talk about how to authorize and access Google APIs. Thanks for stopping by. Stay tuned.