Firebase Auth - Disable a user and prevent him interacting with the backend - firebase

If a user of my app performs some unwanted action, his account may be disabled by a moderator. However, even if disabled, he will be able to use the app if he is already logged in. How can I prevent this?
The code I use to disable a user is within a Cloud Functions and use the following:
admin.auth().updateUser(uid, {
disabled: true
});

Disabling a user's account prevents them from signing in to the app in the future, and prevents their ID token from being refreshed. But their current ID token is still valid for up to an hour.
To detect the disabling of the user account, you can add their ID token to a blocklist and check against that list. You'd typically do that in your security rules, in your server-side code, and (for good measure) in the client. For more on this, see the Firebase documentation on detecting ID token revocation.

Related

Is there a way to log out a specific user using firebase auth go sdk?

background of this question
I'm using firebase auth for user authentication on my app.
I realized that firebase doesn't have a log of user information changes, so I can't answer user questions about it.
So, I'm planning to move the feature of changing user account info (like email, display name, and password) from using the client-side firebase auth library to using server-side firebase auth SDK for the purpose of taking logs of these changes to use for user support. Also, I'd like to make logout a user who changes account info.
I've looked for the appropriate API on the document firebase.google.com/go/v4/auth and found UpdateUser function. The struct UserToUpdate which is a parameter of UpdateUser can set a new email address, new password and new display name, but I can't find to set the parameter to make a user logout.
my question
Is there a way to log out a specific user by firebase auth go SDK?
Firebase Authentication's client-side sign-in is based on ID tokens, which are valid until their built-in expiration (by default: an hour after they are minted). Since no server keeps a list of all the ID tokens it has minted, there is no way to mark a token as invalid on such a list either.
The common approach to revoke access for a user is to:
Revoke the refresh token, so that they can no longer mint new ID tokens with it.
Add the ID token(s) of the user to a self-managed list of revoked ID tokens.
Detect the presence of an ID token in this list from your server-side code and security rules.
Optionally detect the refresh token revocation on the client
Instead of logging the user out, you can also force-refresh their ID token/profile on the client to get the latest information from the server.

How to disable user account in Firebase Web JS SDK?

I am using Firebase Auth to authenticate users using the Email/Password Method. Sometimes I detect spam users that create a lot of accounts from one IP address. I want to block them to protect my app.
I know that there is a method called "Disable User Account" in Firebase Console. I want to use it in my project.
I searched in Stack Overflow as well as the Firebase Docs and found that this only can be done in Admin SDK but I want to use it in the Firebase Web JS SDK. So is there a method to do that like user.DisableAccount?
There is no method to disable a specific user's account in the client-side Firebase SDKs, as that would be a security risk.
But if you look at the documentation for updating a user with the Admin SDK, you'll see there is a property disabled that you can set to true.
From that moment in, that user won't be able to sign in or refresh their ID token. Their existing ID token is still valid though, and by default, that means it may take up to an hour for them to get signed out of your app. If that interval is a concern for your use case, have a look at the documentation on managing user sessions, specifically the section on detecting ID token revocation. While more work, this allows you more granular control of the expiration of the token.

Detect account disable on Firebase Console

Im using Flutter and Firebase. I am trying to figure out if there is a 'built in' way to detect when a Firebase account has been disabled, so that the Flutter app can react and sign out that user if they are logged in already?
I could accomplish this task by adding a 'isDisabled' property to the users document since I already listen for changes to that doc and if it becomes 'true' then log them out. This would require that two changes are made, the 'isDisabled' is set on user doc and account is marked disabled under Authentication.
It just seemed like there might be a more direct way to accomplish this task.
There is not really a more direct way. Firebase Auth is not "realtime". When an account is disabled, the SDK does not know about it immediately. In fact, the user's auth token will stay valid for up to another hour after the time it was disabled. When the token finally expires, the SDK will no long be able to refresh it, and the user will become signed out. Your code will then see that the user is signed out, and they will not be able to sign in again.

How to disallow disposable email in firebase auth email provider signup?

We are using firebase auth and firebase auth UI to authenticate a user.
We want to disallow or block those user's, who is trying to use a temporary mailbox for signing up (eg: https://www.mailinator.com).
There are 2 proposed solutions:
Do a client-side validation for the email ID? (Difficult to manage a blacklist of email providers in the client. Also, people can still use API to hack it).
After the user signs up, on onCreate user event, we can trigger a firebase function to validate the email ID against the blacklist, then we can disable or revoke the account. But here,
if we are disabling the user, he/she will get access to our app for next 1 hour as the client already gained the ID token.
If we are revoking refresh token, we'll have to again wait for 1 hour or write the rule to make a query to Firestore to check if user access is revoked. (Better if we can avoid this query)
Is there a better or native way to solve this issue?
If we are not getting any other solutions, we'll choose to go with 2nd option (revoking refresh token).
I would do a combination of both solutions you proposed. Doing the client side check will trip up most people and for the more tech savvy that try to get around it, your onCreate trigger will deal with them.
You could also add their uid to a blocked list in the realtime database from your onCreate trigger.
Then you can listen to it on the client and log them out. And for database rules you can check if they are in the block list and so block the read/write rule.
a regularly updated service to check DPA is already being maintained.
Do a simple get request to:
https://open.kickbox.com/v1/disposable/{user_email}
this would return the response
{
"disposable": true
}
if email id is disposable.
you can send the get request with complete email id or just the domain.
e.g. https://open.kickbox.com/v1/disposable/jamond67#zdecaesgl.com
or https://open.kickbox.com/v1/disposable/zdecaesgl.com

How to logout the user using Firebase Admin SDK?

So, I have created a cloud function using Firebase Admin SDK. The purpose of that function is to disable the user and after successfully disabling it, I want that user to be logged out from my application. I have disabled user but can't figure out how to log out the user.
I was wondering if there is any function of a workaround to achieve this?
A user that is signed in to your app has a ID token that is valid for up to an hour. Once that token has been created, there is no way to revoke it.
The typical way to handle your use-case is to also flag the user in a server-side database once you disable their account, and then check that flag in any operations.
For example, if your using the Firebase Realtime Database, and disable the user with Node.js, the code to also flag the user in the database could look like this:
// Disable the user in Firebase Authentication to prevent them from signing in or refreshing their token
admin.auth().updateUser(uid, {
disabled: true
}).then(function() {
// Flag the user as disabled in the database, so that we can prevent their reads/writes
firebase.database().ref("blacklist").child(uid).set(true);
});
And you can then check this in the server-side security rules with something like this:
{
"rules": {
".read": "auth.uid !== null && !root.child('blacklist').child(auth.uid).exists()"
}
}
This rule allows all users that are signed in (auth.uid !== null) full read access to the database, but blocks users who you've flagged (!root.child('blacklist').child(auth.uid).exists()).
For an (even) more elaborate example of this approach, see the documentation on session management.
There are two main types of tokens used in Firebase Auth that are relevant to your question here:
Refresh token
ID token (aka, access token)
Firebase ID tokens are short lived and last for an hour; the refresh token can be used to retrieve new ID tokens. Refresh tokens expire only when one of the following occurs:
The user is deleted
The user is disabled
A major account change is detected for the user. This includes events like password or email address updates.
https://firebase.google.com/docs/auth/admin/manage-sessions
So in your case, when you disable the user, the refresh token will be automatically revoked. This means that once the short-lived ID token expires, they won't be able to retrieve a new one.
But you want them to be logged out immediately after being disabled. There are two main considerations here:
if you control the well-behaved client application, you can voluntarily log them out in the client
if you want to truly protect against malicious actors, you can revoke the ID token on the backend
Voluntarily logging out in a well-behaved client
If the token is revoked via the Admin SDK, the client is informed of the revocation and the user is expected to reauthenticate or is signed out:
https://firebase.google.com/docs/auth/admin/manage-sessions#respond_to_token_revocation_on_the_client
However, the docs are very misleading here. There is no built-in behaviour to automatically inform the client of a revocation. Instead, you can follow the suggestions in this thread (https://groups.google.com/g/firebase-talk/c/cJjo9oknG6g/m/XG24x8SqEgAJ) which talk about how to implement this behaviour. The two main options presented are:
Use Firebase Realtime Database to build your own real-time "push" mechanism to detect revocations
Use currentUser.getIdToken(true) to force-fetch a new id token, which will detect the refresh token revocation, and log the user out (you should get an even on the onAuthStateChanged listener).
For option 2, note the parameter true passed in to forceRefresh. This is generally not a good option - you don't want to force refresh on every API request, but if you don't, it's hard to know when to do a force refresh.
When you refresh the page, the Firebase client SDK will typically automatically perform a force refresh.
Server-side detection
When a user's ID token is to be verified, the additional checkRevoked boolean flag has to be passed to verifyIdToken. If the user's token is revoked, the user should be signed out on the client or asked to reauthenticate using reauthentication APIs provided by the Firebase Authentication client SDKs.
https://firebase.google.com/docs/auth/admin/manage-sessions#detect_id_token_revocation_in_the_sdk
Note that using the checkRevoked=true option results in a network request from your backend to Firebase's backend, which is expensive. Again, it's hard to know when it's worth using checkRevoked. Perhaps it's worth the cost to always perform the network check on a small subset of highly sensitive APIs.
Summary
You should read through the docs in full (https://firebase.google.com/docs/auth/admin/manage-sessions) and see which approach suits you best.
Frank van Puffelen has already covered the other standard option - using rules to guard Firebase backend services.
But in general, there isn't anything that helps out of the box. If you understand the concept behind refresh tokens and id tokens, you'll notice that it's fundamentally not possible to revoke the ID token while retaining the performance benefits (ie, reducing network traffic) that is the entire reason for using the refresh+id model to begin with.
I'd just let the token expire, and accept that any "disable" can be delayed by up to 1 hour.

Resources