Why auth testing secures APIs in Postman - Automation Benefits in Action

Verify API authentication protects endpoints

Preconditions (3)

Step 1: Open Postman and create a new request

Step 2: Set the request method to GET and enter the protected API endpoint URL

Step 3: Send the request without any authentication headers

Step 4: Observe the response status code and message

Step 5: Add the valid authentication token in the Authorization header

Step 6: Send the request again

Step 7: Observe the response status code and message

✅ Expected Result: The request without authentication returns 401 Unauthorized or 403 Forbidden. The request with valid authentication returns 200 OK with expected data.

Automation Requirements - Postman with Newman CLI

Assertions Needed:

Verify response status code is 401 or 403 when no auth header is sent

Verify response status code is 200 when valid auth header is sent

Verify response body contains expected data on successful auth

Best Practices:

Use environment variables for tokens

Use pre-request scripts to set auth headers

Use test scripts to assert response status and body

Organize tests in collections for reusability

Automated Solution

Postman

pm.test('Unauthorized request returns 401 or 403', function () {
    pm.response.to.have.status.oneOf([401, 403]);
});

// This test runs only if auth header is present
if (pm.request.headers.has('Authorization')) {
    pm.test('Authorized request returns 200', function () {
        pm.response.to.have.status(200);
    });
    pm.test('Response body contains expected data', function () {
        const jsonData = pm.response.json();
        pm.expect(jsonData).to.have.property('data');
    });
}

This Postman test script checks the API response status and body.

First, it verifies that requests without authentication return 401 or 403 status codes, indicating access is denied.

Then, if the Authorization header is present, it asserts the response status is 200, meaning access is granted.

Finally, it checks the response body contains a 'data' property, confirming the API returned expected content.

Using environment variables for tokens and organizing tests in collections helps keep tests clean and reusable.

Common Mistakes - 3 Pitfalls

{'mistake': 'Not checking the response status code for unauthorized requests', 'why_bad': "Without verifying the status code, you can't be sure the API properly blocks unauthorized access.", 'correct_approach': 'Always assert that unauthorized requests return 401 or 403 status codes.'}

Hardcoding authentication tokens in the test scripts

Not testing both authorized and unauthorized scenarios

Bonus Challenge

Now add data-driven testing with 3 different API tokens: one valid, one expired, and one invalid

Show Hint

Practice

1. Why is authentication testing important for securing APIs?

easy

A. It reduces the API's server costs.

B. It improves the speed of the API response.

C. It changes the API's data format automatically.

D. It verifies that only authorized users can access the API.

Solution

1. Step 1: Understand the purpose of authentication testing

   Authentication testing checks if the API correctly allows only users with valid credentials to access it.

2. Step 2: Identify the security benefit

   By verifying authorized access, it prevents unauthorized users from using the API, protecting sensitive data and functions.

3. Final Answer:

   It verifies that only authorized users can access the API. -> Option D

4. Quick Check:

   Authentication testing = verify authorized access [OK]

Hint: Auth testing checks who can use the API [OK]

Common Mistakes:

• Confusing authentication with performance testing
• Thinking auth testing changes data formats
• Believing auth testing reduces server costs

2. Which Postman feature is used to test API authentication by sending tokens?

easy

A. Tests tab

B. Pre-request Scripts

C. Authorization tab

D. Collection Runner

Solution

1. Step 1: Identify where to set tokens in Postman

   The Authorization tab in Postman allows you to add tokens or credentials to API requests.

2. Step 2: Understand its role in auth testing

   Using the Authorization tab, you can test with valid or invalid tokens to check API security.

3. Final Answer:

   Authorization tab -> Option C

4. Quick Check:

   Token testing uses Authorization tab [OK]

Hint: Set tokens in Authorization tab for auth tests [OK]

Common Mistakes:

• Using Pre-request Scripts to set tokens instead of Authorization tab
• Confusing Tests tab with setting tokens
• Thinking Collection Runner sets tokens automatically

3. Consider this Postman test script snippet:

pm.test('Status is 401', () => {
  pm.response.to.have.status(401);
});

What does this test check when running an API request without a token?

medium

A. The API denies access with status 401 Unauthorized.

B. The API returns success even without a token.

C. The API returns a 200 OK status.

D. The API crashes and returns no response.

Solution

1. Step 1: Analyze the test script

   The script expects the response status code to be 401, which means Unauthorized access.

2. Step 2: Understand the context of no token

   Without a token, the API should deny access, returning 401 to indicate authentication failure.

3. Final Answer:

   The API denies access with status 401 Unauthorized. -> Option A

4. Quick Check:

   Status 401 means unauthorized access denied [OK]

Hint: 401 status means access denied without token [OK]

Common Mistakes:

• Thinking 401 means success
• Confusing 401 with 200 OK
• Assuming API crashes without token

4. You wrote this Postman test to check unauthorized access:

pm.test('Unauthorized status', () => {
  pm.response.to.have.status(403);
});

But the API returns 401 instead. What should you do to fix the test?

medium

A. Change the expected status to 401 in the test script.

B. Change the API to return 403 instead of 401.

C. Remove the test because 403 and 401 are the same.

D. Add a token to the request to avoid 401.

Solution

1. Step 1: Understand HTTP status codes

   401 means Unauthorized (no or invalid token), 403 means Forbidden (no permission).

2. Step 2: Match test to actual API behavior

   The API returns 401, so the test should expect 401 to pass.

3. Final Answer:

   Change the expected status to 401 in the test script. -> Option A

4. Quick Check:

   Test status must match API response [OK]

Hint: Match test status code to API response code [OK]

Common Mistakes:

• Assuming 401 and 403 are interchangeable
• Changing API instead of test script
• Removing test instead of fixing it

5. You want to automate testing an API's authentication using Postman. Which approach best secures the API by testing both valid and invalid tokens?

hard

A. Test only invalid tokens and assume valid tokens work.

B. Create two requests: one with a valid token expecting 200 OK, one with invalid token expecting 401 Unauthorized.

C. Send requests without tokens and ignore the responses.

D. Send only valid tokens repeatedly to check API speed.

Solution

1. Step 1: Understand comprehensive auth testing

   Testing both valid and invalid tokens ensures the API accepts authorized users and rejects unauthorized ones.

2. Step 2: Choose the best Postman approach

   Creating two requests--one with valid token expecting success (200 OK), and one with invalid token expecting failure (401 Unauthorized)--covers both cases.

3. Final Answer:

   Create two requests: one with a valid token expecting 200 OK, one with invalid token expecting 401 Unauthorized. -> Option B

4. Quick Check:

   Test valid and invalid tokens for full auth coverage [OK]

Hint: Test both valid and invalid tokens for security [OK]

Common Mistakes:

• Testing only valid tokens
• Ignoring responses without tokens
• Assuming invalid tokens alone are enough