Token management in variables in Postman - Build an Automation Script

Manage authentication token using Postman variables

Preconditions (2)

Step 1: Send a POST request to the login API with valid username and password in the request body

Step 2: Verify the response status code is 200

Step 3: Extract the token value from the JSON response body

Step 4: Save the extracted token into a Postman environment variable named 'authToken'

Step 5: Send a GET request to a protected API endpoint using the 'authToken' variable in the Authorization header as 'Bearer {{authToken}}'

Step 6: Verify the response status code is 200 and the response body contains expected protected data

✅ Expected Result: The token is correctly saved in the environment variable and used in the Authorization header to access protected API successfully

Automation Requirements - Postman Tests (JavaScript)

Assertions Needed:

Response status code is 200 after login

Token is extracted and saved in environment variable

Protected API request returns status code 200

Protected API response contains expected data

Best Practices:

Use pm.environment.set() to save variables

Use pm.response.json() to parse JSON response

Use pm.test() for assertions

Use environment variables in request headers with {{variableName}} syntax

Keep tests clear and modular

Automated Solution

Postman

/* Login Request Tests */
pm.test('Login status code is 200', () => {
    pm.response.to.have.status(200);
});

const jsonData = pm.response.json();
pm.test('Token is present in response', () => {
    pm.expect(jsonData.token).to.exist;
});

pm.environment.set('authToken', jsonData.token);

/* Protected API Request Tests */
pm.test('Protected API status code is 200', () => {
    pm.response.to.have.status(200);
});

pm.test('Protected API response contains expected data', () => {
    const data = pm.response.json();
    pm.expect(data).to.have.property('protectedData');
    pm.expect(data.protectedData).to.be.a('string').that.is.not.empty;
});

This script is split into two parts for two requests in Postman.

For the login request, it checks the status code is 200, then parses the JSON response to get the token. It asserts the token exists, then saves it to an environment variable authToken using pm.environment.set().

For the protected API request, it uses the saved authToken in the Authorization header as Bearer {{authToken}}. The tests verify the status code is 200 and the response contains the expected protected data property.

This approach ensures the token is dynamically managed and reused securely between requests.

Common Mistakes - 4 Pitfalls

Hardcoding the token value instead of saving it dynamically

Not checking the login response status before extracting token

Using global variables instead of environment variables

{'mistake': 'Not using the token variable in the Authorization header properly', 'why_bad': "If the header is not set with the variable syntax, the token won't be sent correctly", 'correct_approach': "Use the syntax 'Bearer {{authToken}}' in the Authorization header to inject the token"}

Bonus Challenge

Now add data-driven testing with 3 different user credentials to login and verify token management

Show Hint

Practice

1. In Postman, why is it useful to store an authentication token in an environment variable?

easy

A. To make the token visible to all users of the Postman app

B. To encrypt the token for security

C. To automatically refresh the token without any scripting

D. To reuse the token across multiple requests without re-authenticating each time

Solution

1. Step 1: Understand token reuse in Postman

   Storing a token in an environment variable allows multiple requests to access it easily without needing to get a new token each time.

2. Step 2: Evaluate other options

   Making the token visible to all users or automatic refresh without scripting is not true by default. Encryption is not automatic either.

3. Final Answer:

   To reuse the token across multiple requests without re-authenticating each time -> Option D

4. Quick Check:

   Token reuse = B [OK]

Hint: Tokens stored in variables enable reuse across requests [OK]

Common Mistakes:

• Thinking tokens auto-refresh without scripts
• Assuming variables encrypt tokens automatically
• Believing tokens are shared with all users by default

2. Which of the following is the correct way to set a token value to an environment variable in Postman test script?

easy

A. pm.environment.set('token', response.token);

B. pm.setEnvironmentVariable('token', response.token);

C. pm.environment.token = response.token;

D. pm.variables.set('token', response.token);

Solution

1. Step 1: Identify the current Postman syntax for setting environment variables

   The correct method is pm.environment.set('variableName', value) in Postman scripts.

2. Step 2: Check other options for correctness

   pm.setEnvironmentVariable is deprecated, direct assignment is invalid, and pm.variables.set sets local variables, not environment variables.

3. Final Answer:

   pm.environment.set('token', response.token); -> Option A

4. Quick Check:

   Use pm.environment.set() to set env variables [OK]

Hint: Use pm.environment.set('name', value) to set env variables [OK]

Common Mistakes:

• Using deprecated pm.setEnvironmentVariable method
• Trying to assign variables directly like pm.environment.token
• Confusing local and environment variables

3. Given this Postman test script snippet after a login request:

let jsonData = pm.response.json();
pm.environment.set('authToken', jsonData.token);

What will be the value of {{authToken}} in the next request if the response JSON is {"token": "abc123"}?

medium

A. null

B. undefined

C. "abc123"

D. pm.response.json()

Solution

1. Step 1: Extract token from response JSON

   The script gets the token value "abc123" from the response JSON using pm.response.json().token.

2. Step 2: Set environment variable 'authToken'

   The token value "abc123" is stored in the environment variable 'authToken' using pm.environment.set.

3. Final Answer:

   "abc123" -> Option C

4. Quick Check:

   Stored token = "abc123" [OK]

Hint: Stored token equals JSON token value from response [OK]

Common Mistakes:

• Assuming variable is undefined if not explicitly declared
• Confusing variable name with function call
• Expecting null instead of actual token string

4. You wrote this test script to save a token:

let jsonData = pm.response.json();
pm.environment.set('token', jsonData.authToken);

But the token is not saved. What is the most likely reason?

medium

A. You must use pm.variables.set instead

B. The response JSON does not have a key named 'authToken'

C. pm.environment.set is deprecated and does not work

D. Tokens cannot be saved in environment variables

Solution

1. Step 1: Check the JSON key used in script

   The script tries to access jsonData.authToken, so the response must have that key.

2. Step 2: Verify if the response JSON contains 'authToken'

   If the response uses a different key like 'token', jsonData.authToken will be undefined and nothing is saved.

3. Final Answer:

   The response JSON does not have a key named 'authToken' -> Option B

4. Quick Check:

   Key mismatch causes undefined token [OK]

Hint: Check JSON key names match exactly in script [OK]

Common Mistakes:

• Assuming pm.environment.set is deprecated
• Using pm.variables.set for environment variables
• Believing tokens can't be saved in environment variables

5. You want to automatically refresh an expired token in Postman by chaining requests. Which approach correctly manages the token variable for reuse?

hard

A. Use a pre-request script in all requests to check token expiry and request a new token if expired, then update the environment variable

B. Manually update the token variable in Postman UI before each request

C. Store the token in a global variable and never update it

D. Hardcode the token in the request headers and do not use variables

Solution

1. Step 1: Understand token expiry handling

   Tokens expire, so scripts must check expiry and refresh tokens automatically to avoid failures.

2. Step 2: Use pre-request scripts to automate token refresh

   Pre-request scripts can check if the token is expired and call the authentication endpoint to get a new token, then update the environment variable.

3. Step 3: Evaluate other options

   Manual updates are error-prone, global variables without updates cause failures, and hardcoding tokens is insecure and inflexible.

4. Final Answer:

   Use a pre-request script in all requests to check token expiry and request a new token if expired, then update the environment variable -> Option A

5. Quick Check:

   Automate token refresh with pre-request scripts [OK]

Hint: Automate token refresh in pre-request scripts [OK]

Common Mistakes:

• Relying on manual token updates
• Using global variables without refresh logic
• Hardcoding tokens in requests