Role-based access control pattern in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a user role in Firebase rules.

Firebase

match /users/{userId} {
  allow read: if request.auth.token.role == [1];
}

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

A"admin"

B"user"

C"guest"

D"editor"

Attempts:

3 left

💡 Hint

Common Mistakes

Using role names without quotes

Using a role that is not defined in the system

The role "admin" is used here to allow read access only to admin users.

2fill in blank

medium

Complete the code to check if the user has the editor role.

Firebase

allow write: if request.auth.token.role == [1];

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

A"admin"

B"editor"

C"user"

D"guest"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong role for write access

Forgetting to use quotes around the role

The write permission is granted only if the user's role is "editor".

3fill in blank

hard

Fix the error in the role check to allow only admins to delete.

Firebase

allow delete: if request.auth.token.role == [1];

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

A"admin"

B"guest"

C"user"

D"editor"

Attempts:

3 left

💡 Hint

Common Mistakes

Using single '=' instead of '==' for comparison

Using the wrong role string

The equality check must use '==' instead of '=' to compare roles.

4fill in blank

hard

Fill both blanks to allow read for admins and editors only.

Firebase

allow read: if request.auth.token.role == [1] || request.auth.token.role == [2];

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

A"admin"

B"user"

C"editor"

D"guest"

Attempts:

3 left

💡 Hint

Common Mistakes

Using roles that should not have read access

Using '&&' instead of '||' for this condition

This rule allows read access if the user role is either "admin" or "editor".

5fill in blank

hard

Fill all three blanks to allow write only if user is admin and the document owner.

Firebase

allow write: if request.auth.token.role == [1] && resource.data.ownerId == [2] && request.auth.uid == [3];

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

A"admin"

Bresource.data.ownerId

Crequest.auth.uid

D"user"

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking ownership correctly

Using wrong role or variables

This rule ensures that only admins who own the document can write to it.

Practice

1. What is the main purpose of role-based access control (RBAC) in Firebase security rules?

easy

A. To store user data in Firestore

B. To manage user permissions based on their assigned roles

C. To create user authentication tokens

D. To automatically backup database data

Solution

1. Step 1: Understand RBAC concept

   RBAC assigns permissions to users based on their roles, controlling what they can access.

2. Step 2: Identify RBAC purpose in Firebase

   In Firebase, RBAC is used in security rules to allow or deny access depending on user roles.

3. Final Answer:

   To manage user permissions based on their assigned roles -> Option B

4. Quick Check:

   RBAC controls permissions by roles [OK]

Hint: RBAC controls access by user roles, not data storage [OK]

Common Mistakes:

• Confusing RBAC with data storage functions
• Thinking RBAC creates authentication tokens
• Assuming RBAC handles backups

2. Which Firebase security rule syntax correctly checks if a user has the role 'admin' using request.auth.token.role?

easy

A. allow read: if request.auth.token.role == 'admin';

B. allow read: if request.auth.role == 'admin';

C. allow read: if auth.token.role == 'admin';

D. allow read: if request.auth.token == 'admin';

Solution

1. Step 1: Identify correct token path

   The user's role is stored in request.auth.token.role, so the check must use this exact path.

2. Step 2: Match syntax for role check

   The correct syntax compares request.auth.token.role to the string 'admin' using ==.

3. Final Answer:

   allow read: if request.auth.token.role == 'admin'; -> Option A

4. Quick Check:

   Use full path request.auth.token.role == 'admin' [OK]

Hint: Use full path request.auth.token.role for role checks [OK]

Common Mistakes:

• Using request.auth.role instead of request.auth.token.role
• Omitting 'token' in the path
• Comparing token object directly to string

3. Given this Firebase rule snippet:

allow write: if request.auth.token.role == 'editor';

What happens if a user with role 'viewer' tries to write data?

medium

A. The write is allowed because the user is authenticated

B. The write is allowed only if the user has a custom claim

C. The write is denied because the role is not 'editor'

D. The write is denied because the token is missing

Solution

1. Step 1: Analyze the rule condition

   The rule allows write only if request.auth.token.role equals 'editor'.

2. Step 2: Check user's role against condition

   The user has role 'viewer', which does not match 'editor', so the condition fails.

3. Final Answer:

   The write is denied because the role is not 'editor' -> Option C

4. Quick Check:

   Role mismatch denies write [OK]

Hint: Role must exactly match to allow access [OK]

Common Mistakes:

• Assuming any authenticated user can write
• Confusing roles with authentication status
• Ignoring role check in rules

4. Identify the error in this Firebase security rule snippet:

allow read: if request.auth.token.role = 'admin';

medium

A. Using single equals '=' instead of double equals '==' for comparison

B. Missing semicolon at the end of the statement

C. Incorrect property name; should be request.auth.role

D. Using 'allow read' instead of 'allow write'

Solution

1. Step 1: Check comparison operator

   The rule uses '=' which is an assignment operator, not a comparison operator.

2. Step 2: Correct operator for equality check

   Firebase rules require '==' to compare values, so '=' causes a syntax error.

3. Final Answer:

   Using single equals '=' instead of double equals '==' for comparison -> Option A

4. Quick Check:

   Use '==' for comparisons in rules [OK]

Hint: Use '==' for comparisons, '=' is assignment [OK]

Common Mistakes:

• Using '=' instead of '==' in conditions
• Confusing property names in request.auth
• Ignoring syntax errors in rules

5. You want to allow users with roles 'admin' or 'moderator' to delete documents, but only 'admin' can update them. Which Firebase rule snippet correctly implements this?

hard

A. allow delete: if request.auth.token.role == 'admin' || 'moderator';
allow update: if request.auth.token.role == 'admin';

B. allow delete, update: if request.auth.token.role == 'admin' || 'moderator';

C. allow delete: if request.auth.token.role == 'admin' && request.auth.token.role == 'moderator';
allow update: if request.auth.token.role == 'admin';

D. allow delete: if request.auth.token.role in ['admin', 'moderator'];
allow update: if request.auth.token.role == 'admin';

Solution

1. Step 1: Understand role conditions for delete

   Users with role 'admin' or 'moderator' can delete, so use 'in' operator with list ['admin', 'moderator'] for clarity and correctness.

2. Step 2: Understand role condition for update

   Only 'admin' can update, so check equality with 'admin' for update permission.

3. Step 3: Evaluate options

   allow delete: if request.auth.token.role == 'admin' || 'moderator'; allow update: if request.auth.token.role == 'admin'; has syntax error ('|| 'moderator'' invalid); allow delete, update: if request.auth.token.role == 'admin' || 'moderator'; has syntax error with '|| 'moderator''; allow delete: if request.auth.token.role == 'admin' && request.auth.token.role == 'moderator'; allow update: if request.auth.token.role == 'admin'; uses '&&' which requires both roles simultaneously (impossible). allow delete: if request.auth.token.role in ['admin', 'moderator']; allow update: if request.auth.token.role == 'admin'; correctly uses 'in' and separate rules.

4. Final Answer:

   allow delete: if request.auth.token.role in ['admin', 'moderator']; allow update: if request.auth.token.role == 'admin'; -> Option D

5. Quick Check:

   Use 'in' for multiple roles, '==' for single role [OK]

Hint: Use 'in' for multiple roles, '==' for single role check [OK]

Common Mistakes:

• Using '&&' instead of '||' for multiple roles
• Incorrect syntax with '||' and strings
• Trying to check multiple roles with '==' operator