google sign in within web and jwt

I have build my authentication part in my web application by using json web token(jwt). the authentication rules are following: 1. user sign up/sign in with username and password and server auth APIs will return a jwt; 2. client can use the the jwt to access authenticated resource in server side. 3. the server APIs can decode the jwt to get user and judge whether user is existed and user has right to access the resource. I want to add google sign in function in my application. I have read google sign in guide and understand that I can call google sign in oAuth. But I have confusion that when I successfully use google sign in and how to automatic sign up the google account in my application, because I cannot provide the password.