Security Rules and Firebase Authentication

Firebase Security Rules provide access control and data validation in a format that supports multiple levels of complexity. To build user-based and role-based access systems that keep your users' data safe, use Firebase Authentication with Firebase Security Rules.

Identify users

Authentication identifies users requesting access to your data and provides that information as a variable you can leverage in your rules. The auth variable contains the following information:

• uid: A unique user ID, assigned to the requesting user.
• token: A map of values collected by Authentication.

The auth.token variable contains the following values:

If you want to add customized authentication attributes, the auth.token variable also contains any custom claims you specify.

When the user requesting access isn't signed in, the auth variable is null. You can leverage this in your rules if, for example, you want to limit read access to authenticated users — auth != null. However, we generally recommend limiting write access further.

For more information about the auth variable, see the reference documentation for Cloud Firestore, Realtime Database, and Storage.

Leverage user information in rules

In practice, using authenticated information in your rules makes your rules more powerful and flexible. You can control access to data based on user identity.

In your rules, define how the information in the auth variable — the requestor's user information — matches the user information associated with the requested data.

For example, your app may want to make sure users can only read and write their own data. In this scenario, you would want a match between the auth.uid variable and the user ID on the requested data:

service cloud.firestore {
  match /databases/{database}/documents {
    // Make sure the uid of the requesting user matches name of the user
    // document. The wildcard expression {userId} makes the userId variable
    // available in rules.
    match /users/{userId} {
      allow read, update, delete: if request.auth.uid == userId;
      allow create: if request.auth.uid != null;
    }
  }
}

{
  "rules": {
    "users": {
      "$userId": {
        // grants write access to the owner of this user account
        // whose uid must exactly match the key ($userId)
        ".write": "$userId === auth.uid"
      }
    }
  }
}

service firebase.storage {
  // Only a user can upload their file, but anyone can view it
  match /users/{userId}/{fileName} {
    allow read;
    allow write: if request.auth.uid == userId;
  }
}

Define custom user information

You can further leverage the auth variable to define custom fields assigned to your app's users.

For example, assume you want to create an "admin" role that enables write access on certain paths. You would assign that attribute to users, and then leverage it in the rules granting access on the paths.

In Cloud Firestore, you can add a custom field to users' documents and retrieve that field's value with an embedded read in your rules. So, your admin-based rule would look like the following example:

service cloud.firestore {
  match "some_collection/": {
    // Remember that, in Cloud Firestore, reads embedded in your rules are billed operations
    write: if get(/databases/(database)/documents/users/$(request.auth.uid)).data.admin) == true;
    read: if request.auth.uid != null;
  }
}

For Rules in Realtime Database and Storage, create custom claims in Authentication. You can then reference those custom claims using the auth.token variable.

{
  "rules": {
    "some_path/$sub_path": {
      // Create a custom claim for the admin role
      ".write": "auth.uid != null && auth.token.writer == true"
      ".read": "auth.uid != null"
      }
    }
  }

service firebase.storage {
  // Create a custom claim for the admin role
  match /files/{fileName} {
    allow read: if request.auth.uid != null;
    allow write: if request.auth.token.admin == true;
  }
}

To see more examples of basic Rules leveraging Authentication, see Basic Security Rules.