We are building a Worker service that we want to host in a Docker container. This container interacts with the REST APIs for our on-premise SharePoint server. Authentication in SharePoint REST APIs uses Windows authentication.

When I run the code below from Visual Studio Code (using dotnet run on my Windows development machine), the code works without the exception thrown.

var opts = new RestClientOptions("https://sharepoint.domain.local");
opts.Credentials = new NetworkCredential("username", "password", "domain.local");

var spclient = new RestClient(opts);

var req = new RestRequest("_api/lists/getbytitle('MY_LIST')/items", Method.Get);

var resp = spclient.Execute(req);
_logger.LogDebug("Status code {x} returned from API call {y}", resp.StatusCode, resp.ResponseUri);
_logger.LogTrace("Raw response from {url}. Content: {raw}", resp.ResponseUri, resp.Content);

if(!resp.IsSuccessful)
{
    throw new Exception();
}

Now, when I run the same code in the Docker container, the API call is failing and I am getting an Unauthorized status code from the SharePoint REST API, with the following JSON response:

{
  "odata.error": {
    "code": "-2147024891, System.UnauthorizedAccessException",
    "message": {
      "lang": "en-US",
      "value": "Access denied. You do not have permission to perform this action or access this resource."
    }
  }
}

For testing purposes, I am using the same username/password as I use on my DEV machine. I am certain the username and password is provided and not empty.

Any ideas on how to get this working, please?