Login through third parties including Google, Github etc has been an essential requirement for most web applications. The underlying of this process is oauth authentication. The following diagram from Google shows the process of oauth authentication. As you can see, it is a bi-directional communication between the app and the oauth server. The app needs to handle the callback. This is usually done by a backend server. However, you don’t have to have a dedicated backend server for this if what you want is just to get the user’s information from the third party.