CORS testing in Postman

Introduction

CORS testing checks if a website allows safe sharing of resources between different sites. It helps keep your data safe from unwanted access.

When your web app calls an API hosted on a different domain.

When you want to make sure your server allows only trusted websites to access its data.

When debugging errors related to blocked requests in the browser console.

When adding new third-party services that interact with your website.

When testing security rules for cross-site requests.

Syntax

Postman

1. Open Postman.
2. Create a new request.
3. Set the request method (GET, POST, etc.) and URL.
4. Add headers like 'Origin' to simulate cross-origin requests.
5. Send the request.
6. Check the response headers for 'Access-Control-Allow-Origin' and related CORS headers.

The 'Origin' header is important to simulate requests from different websites.

Look for 'Access-Control-Allow-Origin' in the response to see if CORS is enabled.

Examples

This simulates a GET request from 'https://mywebsite.com' to check if the API allows it.

Postman

GET https://api.example.com/data
Headers:
  Origin: https://mywebsite.com

This tests if POST requests from 'https://trustedsite.com' are accepted by the server.

Postman

POST https://api.example.com/submit
Headers:
  Origin: https://trustedsite.com
Body:
  {"name": "Alice"}

Sample Program

This test checks if the API allows requests from 'https://mywebsite.com'. The presence of 'Access-Control-Allow-Origin' with the same origin means CORS is enabled correctly.

Postman

GET https://api.example.com/data
Headers:
  Origin: https://mywebsite.com

// After sending the request in Postman, check response headers:
// Access-Control-Allow-Origin: https://mywebsite.com
// Access-Control-Allow-Methods: GET, POST
// Access-Control-Allow-Headers: Content-Type

Important Notes

Always test with the exact 'Origin' header your web app will use.

Missing or incorrect CORS headers cause browsers to block requests, even if the server responds.

Postman does not enforce CORS, so checking headers is key to verify server behavior.

Summary

CORS testing ensures safe sharing of resources across websites.

Use Postman to simulate cross-origin requests by setting the 'Origin' header.

Check response headers to confirm if CORS is properly configured.

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