This gist shows how using the pre-request script in Postman, a new Oauth-2 token can be obtained using the a refresh token

postman-oauth2-refresh-token.js

/**
** Postman as of the date of this writing does not support auto-refreshing of Oauth-2 tokens.
** This is an exmaple on how in one can refresh their Oauth-2 tokens just using the pre-request scripts.
** Pre-requisites: You need to have a refresh token. You can use the Postman app to get one.
**/

// Set all these variables in an environment or at collection level
let tokenUrl = pm.variables.get('tokenUrl'),
    clientId = pm.variables.get('clientId'),
    clientSecret = pm.variables.get('clientSecret'),
    refreshToken = pm.variables.get('refreshToken'),
    requestOptions = {
      method: 'POST',
      url: tokenUrl,
      body: {
        mode: 'formdata',
        formdata: [
            {
                key: 'grant_type',
                value: 'refresh_token'
            },
            {
                key: 'client_id',
                value: clientId
            },
            {
                key: 'client_secret',
                value: clientSecret
            },
            {
                key: 'refresh_token',
                value: refreshToken
            }
        ]
      }
    };

console.log({ requestOptions });

pm.sendRequest(requestOptions, (err, response) => {
  let jsonResponse = response.json(),
      newAccessToken = jsonResponse.access_token;
      
  console.log({ err, jsonResponse, newAccessToken })
  
  // If you want to persist the token
  pm.environment.set('accessToken', newAccessToken);
  
  // Or if you just want to use this in the current request and then discard it
  pm.variables.set('accessToken', newAccessToken);
});

I have a header prefix and "send as basic auth header" in client authentification . so how to fix this script to match my purpose ? Thank you in advance