Authentication errors in context in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the user is authenticated in the context.

GraphQL

if (!context.[1]) {
  throw new Error('Not authenticated');
}

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

Atoken

Bauth

Cuser

Dsession

Attempts:

3 left

💡 Hint

Common Mistakes

Checking context.auth instead of context.user

Checking context.token which may not be set

Using context.session which might not exist

The context.user property usually holds the authenticated user information. Checking if it exists helps determine if the user is authenticated.

2fill in blank

medium

Complete the code to throw an authentication error with a specific message.

GraphQL

throw new [1]('Authentication failed');

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

ATypeError

BReferenceError

CError

DAuthenticationError

Attempts:

3 left

💡 Hint

Common Mistakes

Using generic Error which is less descriptive

Using TypeError or ReferenceError which are unrelated

Not throwing an error at all

AuthenticationError is a common custom error type used to indicate authentication failures in GraphQL APIs.

3fill in blank

hard

Fix the error in the code to correctly access the authentication token from context headers.

GraphQL

const token = context.req.headers.[1];

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

AAuthorization

Bauthorization

Ctoken

Dauth

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'Authorization' which may be undefined

Using 'auth' or 'token' which are not standard header names

The HTTP header for authentication tokens is usually authorization in lowercase when accessed in Node.js request headers.

4fill in blank

hard

Fill both blanks to extract the token from the authorization header string.

GraphQL

const token = context.req.headers.authorization?.[1](' ')[[2]];

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

Asplit

B1

C0

Djoin

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 0 which returns 'Bearer' instead of the token

Using join instead of split

Not handling the case when authorization is undefined

The authorization header usually has the format 'Bearer TOKEN'. Splitting by space and taking the second part (index 1) extracts the token.

5fill in blank

hard

Fill all three blanks to verify the token and attach the user to context.

GraphQL

const user = await verifyToken([1]);
if (!user) {
  throw new AuthenticationError('Invalid token');
}
context.[2] = user;
return [3];

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

Atoken

Buser

Ccontext.user

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the wrong variable to verifyToken

Not attaching the user to context

Returning context.user instead of user

The token is passed to verifyToken. If valid, the user is attached to context.user. Finally, the user object is returned.

Practice

1. What is the main purpose of checking user information in the GraphQL context during a query?

easy

A. To prevent unauthorized users from accessing sensitive data

B. To speed up the query execution

C. To format the data before sending it

D. To log the query for analytics

Solution

1. Step 1: Understand the role of context in GraphQL

   The context carries user information that helps identify who is making the request.

2. Step 2: Recognize the purpose of authentication checks

   Checking user info in context ensures only authorized users get sensitive data.

3. Final Answer:

   To prevent unauthorized users from accessing sensitive data -> Option A

4. Quick Check:

   Authentication protects data = D [OK]

Hint: Always check user info in context to block unauthorized access [OK]

Common Mistakes:

• Thinking context is for speeding queries
• Assuming context formats data
• Believing context is only for logging

2. Which of the following is the correct way to throw an authentication error inside a GraphQL resolver using context?

easy

A. throw new Error('Not authenticated') without checking context

B. if (context.user) throw new Error('Not authenticated')

C. return 'Not authenticated' without throwing error

D. if (!context.user) throw new Error('Not authenticated')

Solution

1. Step 1: Check user presence in context

   We must verify if context.user exists to confirm authentication.

2. Step 2: Throw error when user is missing

   If no user info, throw an error to stop unauthorized access.

3. Final Answer:

   if (!context.user) throw new Error('Not authenticated') -> Option D

4. Quick Check:

   Throw error if no user = C [OK]

Hint: Throw error only when user info is missing in context [OK]

Common Mistakes:

• Throwing error when user exists
• Not checking context before throwing
• Returning error message instead of throwing

3. Given this resolver snippet:

function resolver(parent, args, context) {
  if (!context.user) {
    throw new Error('Not authenticated');
  }
  return 'Secret Data';
}

What will be the output if context.user is null?

medium

A. null

B. Error: Not authenticated

C. 'Secret Data'

D. undefined

Solution

1. Step 1: Check the condition with context.user null

   Since context.user is null, the condition !context.user is true.

2. Step 2: Understand error throwing behavior

   The resolver throws an error 'Not authenticated' and stops execution.

3. Final Answer:

   Error: Not authenticated -> Option B

4. Quick Check:

   Null user triggers error = A [OK]

Hint: Null or missing user causes error throw [OK]

Common Mistakes:

• Assuming it returns secret data anyway
• Expecting null instead of error
• Confusing error message with return value

4. Identify the error in this resolver code snippet:

function resolver(parent, args, context) {
  if (context.user === undefined) {
    throw new Error('Not authenticated');
  }
  return 'User data';
}

medium

A. Throwing error without message is wrong

B. Return statement is missing

C. It should check if context.user is falsy, not just undefined

D. No error, code is correct

Solution

1. Step 1: Analyze the user check condition

   The code only checks if context.user is exactly undefined, missing null or false cases.

2. Step 2: Explain why broader check is needed

   Users can be null or falsy; checking only undefined misses those cases, allowing unauthorized access.

3. Final Answer:

   It should check if context.user is falsy, not just undefined -> Option C

4. Quick Check:

   Check all falsy user values = B [OK]

Hint: Check all falsy user values, not just undefined [OK]

Common Mistakes:

• Checking only undefined misses null users
• Assuming error message is missing
• Thinking return is missing

5. You want to protect a GraphQL query that returns user profile data. Which approach correctly uses context to throw an authentication error only if the user is not logged in, and returns the profile otherwise?

function getUserProfile(parent, args, context) {
  // Your code here
}

hard

A. if (!context.user) throw new Error('Not authenticated'); return context.user.profile;

B. if (context.user) throw new Error('Not authenticated'); return context.user.profile;

C. return context.user.profile; if (!context.user) throw new Error('Not authenticated');

D. throw new Error('Not authenticated'); return context.user.profile;

Solution

1. Step 1: Check user presence before returning data

   The code must first verify if context.user exists to confirm authentication.

2. Step 2: Throw error if user is missing, else return profile

   If no user, throw error; otherwise, safely return user profile data.

3. Final Answer:

   if (!context.user) throw new Error('Not authenticated'); return context.user.profile; -> Option A

4. Quick Check:

   Check user first, then return profile = A [OK]

Hint: Check user before return; throw error if missing [OK]

Common Mistakes:

• Throwing error when user exists
• Returning before checking user
• Throwing error unconditionally