Tell the authorization providers about your app

Before we ask an authorization provider to help our users sign in, we must tell them about our application. Most providers have some kind of web tool or console where you can create applications to kick this process off. Here's one from Google:

In order to identify the client application, we need to create a client ID and secret. Despite the fact that OAuth2 is an open standard, each provider has their own language and mechanism to set things up. Therefore, you will most likely have to play around with the user interface or the documentation to figure it out in each case.

At the time of writing, in Google Cloud Console, you navigate to API Manager and click on the Credentials section.

In most cases, for added security, you have to be explicit about the host URLs from where requests will come. For now, since we're hosting our app locally on localhost:8080, you should use it. You will also be asked for a redirect URI that is the endpoint in our...