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Assigning Roles To Users With Cloud Firestore Security Rules In Firebase

This dev doc guide is best suited for anyone who has been using firebase cloud firestore for a while i.e intermediate to expert level of experience.

If you are a beginner or would want to try out the magic with cloud firestore for web, get started in this codelab here

Adding a user in the "users" collection

You may have for example, a cloud function that adds a user into the users collection on first time authentication as shown below;

Tip ; remember to split up your cloud functions // it's safer and good practice to do that.


    // create a users' doc on first authentication
    const addUser = (userData, context) => {
       return db.collection('users').doc(userData.uid).set({
         displayName: userData.displayName,
         isAdmin : false
    }).catch(console.error);
    };
    module.exports = {
    authOnCreate: functions.auth.user().onCreate(addUser),
    };
 

The "users" collection created on deploying this function would be as in the image below

cloud firestore
Users Collection

Allowing Write permission to Admins only

You check the users collection in firebase cloud firestore database if the user's assigned role evaluates to true, i.e isAdmin:true ;

Note : In this case we're specifying that the Admins to read and write to the posts collection.

 
    service cloud.firestore {
      match /databases/{database}/documents {
        match / posts/{post} {
          allow read;
          allow write : if get(/databases/$(database)/documents/users/$(request.auth.uid))
          .data.isAdmin == true;
          }
      }
    }
    

This is a "low-level" showcase on how to implement role-based data access in firebase cloud firestore, assuming there's no an admin ui or panel.

Learn more about firebase cloud firestore security rules in this awesome firebase doc

Note : When you deploy security rules using the Firebase CLI, the rules defined in your project directory overwrite any existing rules in the Firebase console.

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