SharePoint Server 2019 on-premise REST API Authentication

Question

I need to read list data from SharePoint 2019 on-premise server, from an external server. I have tried calling the REST API but I am having trouble authenticating.

Things I have tried:

• Calling REST endpoint with Network Credentials:

   var client = new RestClient(url);
   var request = new RestRequest(Method.GET) { Credentials = new NetworkCredential("username", "password", "domain") };
   var response = client.Execute(request);
   return response.Content;
  

I am getting 403 response in this case.

• I was successful with a cookie I obtained when accessing the site from the browser (this is not a solution):

   var client = new RestClient(url);
   var request = new RestRequest(Method.GET);
   request.AddHeader("Cookie", "cookie-value");
   return response.Content;
  

What kind of authentication is needed to perform calls to SharePoint REST API? I have also looked up custom Add-Ins, but can only find documentation for SharePoint Online.