Postman's Pre-request Script

postman_oauth_auto_access_token.js

/*
    NOTES
    replace your http://your.oauth.server.domain/oauth/token with actual token url for your oauth server
    replace your_client_id with actual client id of your oauth server
    replace your_client_secret with actual client secret of your oauth server
    replace "your scopes space seperated" with actual scopes
*/

const postRequest = {
  url: "http://your.oauth.server.domain/oauth/token",
  method: 'POST',
  header: {
    'Accept': 'application/json',
    'Content-Type': 'application/x-www-form-urlencoded'
  },
  body: {
      mode: 'urlencoded',
      urlencoded: [
        {key: "grant_type", value: "client_credentials", disabled: false},
        {key: "client_id", value: "your_client_id", disabled: false},
        {key: "client_secret", value: "your_client_secret", disabled: false},
        {key: "scope", value: "your scopes space seperated", disabled:false}
      ]
  }
};
console.log("start pre request script for your oauth protected API");
// uncomment for debug purpose
//console.log(JSON.stringify(postRequest));

pm.sendRequest(postRequest, function (err, response) {
    var responseData = response.json();
	// uncomment for debug purpose
	//console.log("access_token is ---> "+responseData["access_token"]);
	pm.environment.set("access_token",responseData["access_token"]);
});

console.log("end pre request script for your oauth protected API");