Postman pre-request script to get Cognito access token

postman_pre_request.js

pm.sendRequest({
    url: "https://YOUR_COGNITO_DOMAIN_NAME_HERE.auth.eu-west-1.amazoncognito.com/oauth2/token",
    method: 'POST',
    header: {
        'Content-Type': 'application/x-www-form-urlencoded'
    },
    body: {
        mode: 'urlencoded',
        urlencoded: [
            {
                key: "grant_type",
                value: "client_credentials"
            },
            {
                key: "client_id",
                value: "YOUR_CLIENT_ID_HERE"
            },
            {
                key: "client_secret",
                value: "YOUR_CLIENT_SECRET_HERE"
            },
            {
                key: "scope",
                value: "YOUR_SCOPE_HERE"
            }
        ]
    }
}, (err, res) => {
    pm.collectionVariables.set("access_token", res.json().access_token)
});