That is default behavior. You will need credentials to access the REST Services and you have create a Digest to do this programmatically:
String retVal = "";
try
{
string url = "https://YourSite.com/";
HttpClient client = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true });
client.BaseAddress = new System.Uri(url);
string cmd = "_api/contextinfo";
client.DefaultRequestHeaders.Add("Accept", "application/json;odata=verbose");
client.DefaultRequestHeaders.Add("ContentType", "application/json");
client.DefaultRequestHeaders.Add("ContentLength", "0");
StringContent httpContent = new StringContent("");
var response = client.PostAsync(cmd, httpContent).Result;
if (response.IsSuccessStatusCode)
{
string content = response.Content.ReadAsStringAsync().Result;
JsonObject val = JsonValue.Parse(content).GetObject();
JsonObject d = val.GetNamedObject("d");
JsonObject wi = d.GetNamedObject("GetContextWebInformation");
retVal = wi.GetNamedString("FormDigestValue");
}
}
catch
{ }
return retVal;
If you have an account that can access the list in SharePoint then you should be able to use that same account to authenticate against the REST Service and retrieve the list items once you pass it the Digest. If you get one I have a lot of code examples on my blog for this type of application.