Creating a Postman pre-script to set tokens

This post details dives into devloping a pre-request script in Postman that obtains an access token from the authentication server using the client credentials grant

1. Define ID’s and secrets

First we define required credentials to generate an access token.

// Set your credentials
var clientId = 'xxxxxxxxxxxxxxxxxxxxxxxxx'
var clientSecret = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'

2. Build request URL and parameters

Next we build out the request URL, headers and request body

// Set the URL and request parameters
var url = 'https://xxx-xxx.xxxxxxxx.com/oauth2/token'
var headers = {
	'Content-Type': 'application/x-www-form-urlencoded',
	Authorization: 'Basic ' + btoa(clientId + ':' + clientSecret)
}

// Set the request body
var body = {
	mode: 'urlencoded',
	urlencoded: [{ key: 'grant_type', value: 'client_credentials' }]
}

3. Send the post request with pm.sendRequest

Next we make a request using pm.sendRequest function with our defined url, headers and body

// Send the POST request
pm.sendRequest({
    url: url,
    method: 'POST',
    header: headers,
    body: body,
    secure: true
}, function (err, res) {
    // Handle the error
    if (err) {
        console.error('Error:', err);
        return;
    }

4. Extract the accessToken and set with pm.environment.set

Using the returned response, we can now save and set the global variable accessToken with postman’s pm.environment.set function

// Extract and save accessToken as a variable
var jsonResponse = res.json()
if (jsonResponse && jsonResponse.access_token) {
	pm.environment.set('accessToken', jsonResponse.access_token)
	console.log('Access Token saved:', pm.environment.get('accessToken'))
}