Authentication-based rules in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to allow read access only if the user is authenticated.

Firebase

allow read: if request.auth [1];

Drag options to blanks, or click blank then click option'

A=== false

B!== true

C== null

D!= null

Attempts:

3 left

💡 Hint

Common Mistakes

Using '== null' which allows unauthenticated users.

Using strict equality with booleans which is invalid here.

In Firebase rules, request.auth != null means the user is signed in.

2fill in blank

medium

Complete the code to allow write access only if the user's UID matches the document ID.

Firebase

allow write: if request.auth.uid [1] resource.id;

Drag options to blanks, or click blank then click option'

A==

B>

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' which denies access to the owner.

Using comparison operators like '<' or '>' which are invalid here.

Users can write only to their own documents, so UID must equal document ID.

3fill in blank

hard

Fix the error in the rule to allow read access only if the user is authenticated and email is verified.

Firebase

allow read: if request.auth [1] request.auth.token.email_verified == true;

Drag options to blanks, or click blank then click option'

A==

B||

C&&

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '||' which allows access if only one condition is true.

Using '==' or '!=' which are comparison operators, not logical.

Both conditions must be true, so use logical AND '&&'.

4fill in blank

hard

Fill both blanks to allow write access only if the user is authenticated and their role is 'admin'.

Firebase

allow write: if request.auth [1] && request.auth.token.role [2] 'admin';

Drag options to blanks, or click blank then click option'

A!= null

B==

C!=

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!= null' for authentication check.

Using '||' instead of '&&' which weakens the condition.

User must be signed in (request.auth != null) and have role 'admin' (request.auth.token.role == 'admin').

5fill in blank

hard

Fill all three blanks to allow read access only if the user is authenticated, email is verified, and the document's owner field matches the user's UID.

Firebase

allow read: if request.auth [1] && request.auth.token.email_verified == true [2] resource.data.owner [3] request.auth.uid;

Drag options to blanks, or click blank then click option'

A!= null

B&&

C==

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using '||' which allows access if any condition is true.

Using '!=' instead of '==' for ownership check.

All three conditions must be true: user signed in, email verified, and user owns the document.

Practice

1. What does the Firebase rule condition request.auth != null check for?

easy

A. If the request is from a mobile device

B. If the user has admin privileges

C. If the user is signed in

D. If the database is empty

Solution

1. Step 1: Understand the meaning of request.auth

   request.auth holds authentication info if a user is signed in; otherwise, it is null.

2. Step 2: Interpret the condition request.auth != null

   This condition is true only when a user is signed in, meaning authentication info exists.

3. Final Answer:

   If the user is signed in -> Option C

4. Quick Check:

   Authentication check = user signed in [OK]

Hint: Check if request.auth is not null to confirm user login [OK]

Common Mistakes:

• Thinking it checks for admin rights
• Assuming it checks device type
• Confusing with database content check

2. Which of the following is the correct Firebase rule syntax to allow read access only to authenticated users?

easy

A. allow read: if request.auth == true;

B. allow read: if request.auth == null;

C. allow read: if request.auth.id == null;

D. allow read: if request.auth != null;

Solution

1. Step 1: Identify the correct condition for authenticated users

   The condition request.auth != null means the user is signed in.

2. Step 2: Match the syntax with the correct condition

   allow read: if request.auth != null; uses allow read: if request.auth != null; which correctly allows reads only for signed-in users.

3. Final Answer:

   allow read: if request.auth != null; -> Option D

4. Quick Check:

   Correct syntax for auth check = allow read: if request.auth != null; [OK]

Hint: Use != null to allow only signed-in users [OK]

Common Mistakes:

• Using == null which allows unauthenticated users
• Checking request.auth.id instead of request.auth
• Using boolean true instead of null check

3. Given this Firebase rule snippet:

allow read: if request.auth != null && request.auth.uid == resource.data.ownerId;

What happens if a signed-in user tries to read data where ownerId is different from their uid?

medium

A. Read access is denied

B. Read access is granted only if user is admin

C. Read access is granted

D. Read access causes a syntax error

Solution

1. Step 1: Analyze the rule condition

   The rule requires the user to be signed in and their user ID (uid) to match the data's ownerId.

2. Step 2: Evaluate the scenario where uid differs from ownerId

   Since the IDs do not match, the condition fails, so access is denied.

3. Final Answer:

   Read access is denied -> Option A

4. Quick Check:

   User ID match required = access denied if no match [OK]

Hint: User ID must match ownerId for access [OK]

Common Mistakes:

• Assuming any signed-in user can read
• Thinking admin rights are checked here
• Confusing syntax error with logic denial

4. Identify the error in this Firebase rule:

allow write: if request.auth.uid = resource.data.ownerId;

medium

A. Missing check for request.auth != null

B. Using single equals (=) instead of double equals (==)

C. Incorrect field name 'ownerId'

D. No error, rule is correct

Solution

1. Step 1: Check the comparison operator

   The rule uses a single equals = which is an assignment, not a comparison.

2. Step 2: Correct operator usage in Firebase rules

   Firebase rules require double equals == for equality checks.

3. Final Answer:

   Using single equals (=) instead of double equals (==) -> Option B

4. Quick Check:

   Use == for comparisons, not = [OK]

Hint: Use == for equality, not = [OK]

Common Mistakes:

• Confusing assignment (=) with comparison (==)
• Ignoring null check for request.auth
• Assuming field names cause error

5. You want to write a Firebase rule that allows users to update their own profile only if they are signed in and the profile's userId matches their uid. Which rule correctly implements this?

hard

A. allow update: if request.auth != null && request.auth.uid == resource.data.userId;

B. allow update: if request.auth != null && request.auth.uid == request.resource.data.userId;

C. allow update: if request.auth == null || request.auth.uid != resource.data.userId;

D. allow update: if request.auth != null && request.auth.uid == resource.data.ownerId;

Solution

1. Step 1: Understand the difference between resource.data and request.resource.data

   resource.data is the existing data; request.resource.data is the new data being written.

2. Step 2: Match user ID with existing data's userId during update

   To allow update only if the profile's existing userId matches the user's uid, compare request.auth.uid with resource.data.userId.

3. Step 3: Verify the condition

   allow update: if request.auth != null && request.auth.uid == resource.data.userId; correctly checks the user is signed in and owns the existing profile.

4. Final Answer:

   allow update: if request.auth != null && request.auth.uid == resource.data.userId; -> Option A

5. Quick Check:

   Check existing data userId matches auth.uid for update [OK]

Hint: Use resource.data for existing ownership checks [OK]

Common Mistakes:

• Using request.resource.data (new data) instead of resource.data (existing data)
• Allowing updates without authentication
• Using wrong field names for user ID