Adding account linking to my Actions on Google app

Question

I created a Actions on Google app with the Actions SDK. For this i used as said before the Actions SDK, firebase function for the fulfillment and firestore for storing data. All works fine.

Now i want to implement account linking to provide user specific information. I start to read the full documentation for account linking with the refers to integrate a Oauth 2.0 Server and soon. That is my first time i working with account linking and Oauth servers and now i'm totally confused. I don't understand where my auth server have to sit, how to setup it and what parameters it have to process. After reading more and searching for results i found that firebase provide Account authentication. Is it right that this firebase product is similar a Oauth server?

My next big problem is how to enabling account linking in my Actions app. In the Actions on Google documentation i found a topic how to expand the Action Package for account linking. My problem is to unterstand which information the probiertes need.

So summary, if the firebase authentication is really a Oauth server what i need to do that my app and firebase authentication works together.

Maybe everyone knows a good website for understanding the process of account linking and how it can be implemented.

UPDATE 1:

After getting the first answer for my question i started studying more about account linking and the authentication process.

After this i created following roadmap:

1. Create an website with a google account sing-in form and host it with firebase hosting
2. Set up the Oauth2 server
3. Interact with the linked account. Save account informations in my firestore database

So i started with step one. In the firebase authentication documentation i find a example for a google login form. After modifying and hosting the example i try it. It works fine. After sing in by using the hosted website, my google account linked with my project. I checked this in my google account settings. Also the example response with a lots of data like the profile name, email address and so on. So my question at this point is. Why do i have to set up a OAuth server now? After sign in with the example form i linked my account to my project successful. And so i can start saving the received data in my firebase database and act with them in my Actions app.

UPDATE 2:

Okay . Maybey i have a general problem of understanding the right use of account linking. I try to identify the user who use my action to offer special content when he comes back next time. Or maybe create a question with his name from his google account inside the question. So in my understanding i have to link the users google account with my action and save the account information in a database to identify the use next time. So is account linking for this task the right way?

Answer 1

No, Firebase Authentication is not an OAuth2 server.

Firebase Authentication provides a way for you to manage user accounts for your Firebase-based web or mobile app. With the Auth UI it gives a way for users to log into that account using a variety of means (including their Google account, Facebook account, or phone number). It does not, however, provide components that an OAuth2 server provides.

Most notably, it does not provide any way for a user to log in through another client (like the Google Assistant) to gain authorization for that client. You cannot, with Firebase Authentication, issue a token to the Assistant, nor accept a token from the Assistant and verify if this is a user inside Firebase Authentication.

You need to build these components yourself. Google describes the minimum tasks that it needs to do as part of this authentication. You can use Firebase Authentication as part of this as you build such a server (for example, it is a great way to have people log in to their account and for you to verify that account), and it is reasonable to use a Firebase Database to store user tokens if you go that route, Firebase Functions might be a useful place to implement the token exchange point, and Firebase Hosting would be good to host the login page itself - but you'd need to write code that "puts it all together".

Your auth server can sit anywhere. As I said - you can do it through Firebase Functions, but you don't have it. It just needs to be able to provide some responses through web URLs at HTTPS endpoints.

Once you have done this, you need to configure the endpoints on the actions console and implement a request for account linking in your code or in the action package.

Response to Update 1

After sing in by using the hosted website, my google account linked with my project. I checked this in my google account settings.

From an OAuth perspective - no, the Google Account is not "linked" to your project.

Google has issued a token to you (that is to say, the service that you've written) that gives your service access to certain resources. Those resources include information about a particular user.

This may sound like I'm splitting semantics, but it isn't. It is fundamental to what OAuth is offering and what it means when you get an issue a token. You currently have authorization to do certain things.

Why do i have to set up a OAuth server now? After sign in with the example form i linked my account to my project successful. And so i can start saving the received data in my firebase database and act with them in my Actions app.

You haven't linked your account. You have permission to do certain things.

Furthermore, aside from "that's how they do it", you need to setup an OAuth server because you now need to do the same thing for Google - give them permission to do specific things on your server (like use it). Normally this would be involved with "logging in".

Account Linking is really a fancy term for "logging in". You need a way for users to be able to log into your server. You have an access token, but that is roughly the equivalent of having logged into Google's server.

So why do so many websites, for example, have things like "Log In using Google" or "Log In using Facebook"? Because those sites are willing to trust that if their servers can get permitted to certain information at Google or Facebook, then they can trust you. And you might be willing to accept that when they login to your site (either through the web or through Actions), but the Assistant can't assume that. They need to make sure users actually log into your site - that user's deliberately want to do so and that you deliberately want to let them in.