CORS testing in Postman - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding CORS Preflight Requests

Which HTTP method is used by browsers to send a CORS preflight request before the actual request?

A OPTIONS

B GET

C POST

D HEAD

💡 Hint

Think about a method that checks permissions without sending data.

Browsers use the OPTIONS method to send a preflight request to check if the actual request is safe to send.

❓ Predict Output

intermediate

CORS Response Header Behavior

What will be the value of the Access-Control-Allow-Origin header in the response if the server sets it to *?

Postman

GET /api/data HTTP/1.1
Host: example.com
Origin: https://client.com

Response Headers:
Access-Control-Allow-Origin: *

A The browser allows requests from any origin.

B The browser ignores the header and blocks the request.

C The browser allows requests only from https://client.com.

D The browser blocks requests from all origins.

💡 Hint

Consider what the wildcard * means in CORS headers.

The * value means the server allows requests from any origin.

❓ assertion

advanced

Validating CORS Headers in Postman Tests

Which Postman test script correctly asserts that the Access-Control-Allow-Origin header equals https://client.com?

A pm.test('CORS header is correct', () => { pm.response.to.have.header('Access-Control-Allow-Origin', 'https://client.com'); });

B pm.test('CORS header is correct', () => { pm.expect(pm.response.headers.get('Access-Control-Allow-Origin')).to.equal('https://client.com'); });

C pm.test('CORS header is correct', () => { pm.response.headers.has('Access-Control-Allow-Origin', 'https://client.com'); });

D pm.test('CORS header is correct', () => { pm.expect(pm.response.headers.get('Access-Control-Allow-Origin')).to.be.true; });

💡 Hint

Look for the correct way to get a header and compare its value in Postman tests.

Option B correctly retrieves the header value and asserts equality using pm.expect.

🔧 Debug

advanced

Diagnosing CORS Failure in Postman

You send a request from Postman to a server and receive a 200 OK response, but your browser shows a CORS error. Why does this happen?

A The browser caches old CORS headers causing the error.

B The server is blocking Postman requests but allowing browsers.

C Postman automatically adds CORS headers, browsers do not.

D Postman does not enforce CORS, but browsers do.

💡 Hint

Think about how Postman and browsers handle CORS differently.

Postman is a testing tool and does not enforce CORS restrictions, but browsers enforce CORS for security.

❓ framework

expert

Automating CORS Tests in Postman Collection

Which approach best automates testing that a server correctly handles CORS preflight requests in a Postman collection?

A Use Postman to disable CORS enforcement and verify server response status only.

B Send a GET request without Origin header and check for Access-Control-Allow-Origin in response.

C Create a request with method OPTIONS, set Origin header, and assert Access-Control-Allow-* headers in test scripts.

D Send a POST request with Origin header and assert response body contains CORS headers.

💡 Hint

Remember how browsers perform preflight checks and what headers are involved.

Preflight requests use OPTIONS method with Origin header; tests should verify Access-Control-Allow headers in response.

Practice

1. What is the main purpose of CORS testing in Postman?

easy

A. To verify if a server allows resource sharing from different origins

B. To check if the server is running the latest software version

C. To test the speed of the API response

D. To validate the syntax of the API request

Solution

1. Step 1: Understand CORS concept

   CORS (Cross-Origin Resource Sharing) controls if a server permits requests from different websites (origins).

2. Step 2: Relate to Postman testing

   In Postman, testing CORS means checking if the server allows resource sharing from other origins.

3. Final Answer:

   To verify if a server allows resource sharing from different origins -> Option A

4. Quick Check:

   CORS testing = verify cross-origin sharing [OK]

Hint: CORS is about sharing resources across websites [OK]

Common Mistakes:

• Confusing CORS with API speed testing
• Thinking CORS checks server software version
• Assuming CORS validates request syntax

2. Which header should you set in Postman to simulate a cross-origin request for CORS testing?

easy

A. Accept-Encoding

B. Authorization

C. Content-Type

D. Origin

Solution

1. Step 1: Identify header for cross-origin requests

   The Origin header tells the server which website is making the request.

2. Step 2: Use in Postman

   Setting the Origin header in Postman simulates a request from that origin for CORS testing.

3. Final Answer:

   Origin -> Option D

4. Quick Check:

   Set Origin header to test CORS [OK]

Hint: Set 'Origin' header to mimic browser cross-site requests [OK]

Common Mistakes:

• Using Authorization header instead of Origin
• Confusing Content-Type with Origin
• Not setting any header for CORS simulation

3. You send a request in Postman with header Origin: https://example.com. The server responds with header Access-Control-Allow-Origin: https://example.com. What does this response indicate?

medium

A. The server allows requests only from https://example.com

B. The server has a syntax error in headers

C. The server allows requests from any origin

D. The server denies requests from https://example.com

Solution

1. Step 1: Understand Access-Control-Allow-Origin header

   This header specifies which origin the server allows for cross-origin requests.

2. Step 2: Match response header with request origin

   The server's response matches the request origin exactly, meaning it allows requests only from that origin.

3. Final Answer:

   The server allows requests only from https://example.com -> Option A

4. Quick Check:

   Matching Access-Control-Allow-Origin means allowed origin [OK]

Hint: Matching Access-Control-Allow-Origin means allowed origin [OK]

Common Mistakes:

• Thinking it denies the origin when it matches
• Assuming wildcard '*' when specific origin is set
• Confusing syntax error with valid header

4. You test CORS in Postman by setting Origin: https://myapp.com, but the server response lacks Access-Control-Allow-Origin header. What is the likely issue?

medium

A. The request method is invalid

B. The server does not support CORS or is misconfigured

C. Postman does not send the Origin header correctly

D. The server is down

Solution

1. Step 1: Check server response headers for CORS

   If Access-Control-Allow-Origin is missing, the server likely does not allow cross-origin requests.

2. Step 2: Rule out Postman or request issues

   Postman sends headers correctly; missing header usually means server misconfiguration or no CORS support.

3. Final Answer:

   The server does not support CORS or is misconfigured -> Option B

4. Quick Check:

   Missing Access-Control-Allow-Origin means no CORS support [OK]

Hint: Missing Access-Control-Allow-Origin means server blocks CORS [OK]

Common Mistakes:

• Blaming Postman for missing headers
• Assuming request method causes missing header
• Thinking server is down without checking status

5. You want to test if a server allows CORS requests from multiple origins using Postman. Which approach is best to verify this?

hard

A. Send requests with random headers and check response time

B. Send one request without Origin header and check server status

C. Send multiple requests with different Origin headers and check Access-Control-Allow-Origin in each response

D. Send requests only from localhost and assume all origins are allowed

Solution

1. Step 1: Understand testing multiple origins

   To test multiple origins, you must simulate requests from each origin by setting the Origin header accordingly.

2. Step 2: Verify server response for each origin

   Check if Access-Control-Allow-Origin matches the requested origin or allows all origins (wildcard).

3. Final Answer:

   Send multiple requests with different Origin headers and check Access-Control-Allow-Origin in each response -> Option C

4. Quick Check:

   Test each origin with Origin header and check response [OK]

Hint: Test each origin separately by changing Origin header [OK]

Common Mistakes:

• Testing without Origin header
• Assuming localhost tests all origins
• Checking unrelated headers or response time