When you are building a chrome extension, you may need to authenticate the user with a third party service. If the third party service is google itself, it’s relatively easy as you can use google cloud platform plus firebase to authenticate the user. However if you are using other third party service, it’s a bit tricky and there are very few resources available online. I recently built a chrome extension that needs to authenticate the user with Notion and I would like to share my experience here.

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.