Actually iam a new PHP Learner, i developed an web app using Bootstrap, PHP, Mysql. Now i want to give login access for gmail id's which are already existed in my database, so i used login with google API, but want deny login access for any other gmails which are not existed in my database.

You can do this with Google's OAuth 2.0 API. Daniel11 seems to be going around linking to tutorials on his own website, but in this case, it's not entirely applicable because you're looking for information on doing it in PHP, and Daniel's tutorial implements C#.NET. Additionally, it talks about the Contacts API, which I think is not the one you want. You want the Google Sign-In platform, as so: