401 Error Consuming REST service from code but works in browser

Question

I am trying to consume a REST service from another company. When I use the link in the browser it works fine. However I get the 401 error when accessing from code. What am I doing wrong? Do I need to add something to the web.config of the web app?

        string URL = @"https://hdapps-qa.homedepot.com/MYTHDPassport/rs/identity/isSessionValid?thdsso=TEST&callingProgram=PSC&Submit=Submit";
        HttpWebRequest req = WebRequest.Create(URL)
                             as HttpWebRequest;
        string result = null;
        req.Method = "GET";
        req.UseDefaultCredentials = true;
        req.PreAuthenticate = false;
        req.Credentials = CredentialCache.DefaultCredentials;
        using (HttpWebResponse resp = req.GetResponse()
                                      as HttpWebResponse)
        {
            StreamReader reader =
                new StreamReader(resp.GetResponseStream());
            result = reader.ReadToEnd();
        }

Answer 1

A 401 error is caused when you do not have the right permissions to access the url. See here for more information about 401 errors.

It looks like you're trying to access the Home Depot API, or some sort of system related to them. Many APIs require that you send along an authentication token that is typically generated when you create a developer account or is provided to you when you try to register with them. This authentication token is sent along via GET or POST along with the data to the url you're trying to access. This is not always the case - sometimes tokens are stored via cookies or some other storage method that allows access (this may be the case since accessing the url on my machine doesn't work but it does for yours - you might have some sort of token being accessed elsewhere).

These considerations are application specific, so the details of what that token might be and how it is accessed (if that's the problem) rests with the system you're trying to access.

Answer 2

Figured it out. The REST Service is returning a response code of 401 if the session is not valid. So I am catching that exception and handling it. Thanks.