Needs to Get access code without prompt the login screen.

You need the user to login to their account via secure.myob.com to authenticate and retrieve the access code initially.  After that you can use the access token and refresh token without the user re-authenticating via the website.

I need to do the same, as I am trying to connect to MYOB via an Azure function.

This is the code that MYOB have published - 

var developerKey = "YOUR API KEY";
var developerSecret = "YOUR API SECRET";

var configuration = new ApiConfiguration(developerKey, developerSecret, "http://desktop");
var oauthService = new OAuthService(configuration);
var tokens = oauthService.GetTokens(OAuthLogin.GetAuthorizationCode(configuration)); 
var keystore = new SimpleOAuthKeyService();keystore.OAuthResponse = tokens;

// Get Company Files 
var cfService = new CompanyFileService(configuration, null, keystore);
var companyFiles = cfService.GetRange();

The problem is the GetAuthorizationCode function as that function opens the MYOB login page and returns the authorization code via the HTML. 

Surely there must be another way to generate the code?