Writing a Secure WCF Data Service for Excel PowerPivot [closed]

Question

I'm having some trouble writing a secure WCF data service to be consumed by PowerPivot. The service works fine, and I can consume the data in PowerPivot without trouble.

My issue is that when I enter the user ID and password for the Data Feed in PowerPivot (in Data Feed advanced settings), I can't seem to get any access to them from inside the WCF service. I'd like to use both the user ID and password to authenticate against a database, but I need to get at them first. :)

Are there any good examples of how to write a secure WCF Data Service specifically for PowerPivot?

Thanks very much.

Answer 1

I was struggling with this same thing, and after some research found this blog post that got me rolling:

http://pfelix.wordpress.com/2011/04/21/wcf-web-api-self-hosting-https-and-http-basic-authentication/

In short, there is some work you need to do to allow the Principal to flow through to the service call.

Answer 2

There's a full downloadable sample on MSDN

WCF Data Service with basic authentication for PowerPivot clients

https://code.msdn.microsoft.com/office/WCF-Data-Service-with-547e9341

Update

Okay, now I've used the code in the link (that I was researching at the time I posted) I know that it works, so here's the code example:

Step 1: Write an HTTP handler to handle all requests and perform the authentication (or issuance of a 401 challenge).

namespace WebHostBasicAuth.Modules
{
    public class BasicAuthHttpModule : IHttpModule
    {
        private const string Realm = "My Realm";

        public void Init(HttpApplication context)
        {
            // Register event handlers
            context.AuthenticateRequest += OnApplicationAuthenticateRequest;
            context.EndRequest += OnApplicationEndRequest;
        }

        private static void SetPrincipal(IPrincipal principal)
        {
            Thread.CurrentPrincipal = principal;
            if (HttpContext.Current != null)
            {
                HttpContext.Current.User = principal;
            }
        }

        // TODO: Here is where you would validate the username and password.
        private static bool CheckPassword(string username, string password)
        {
            return username == "user" && password == "password";
        }

        private static void AuthenticateUser(string credentials)
        {
            try
            {
                var encoding = Encoding.GetEncoding("iso-8859-1");
                credentials = encoding.GetString(Convert.FromBase64String(credentials));

                int separator = credentials.IndexOf(':');
                string name = credentials.Substring(0, separator);
                string password = credentials.Substring(separator + 1);

                if (CheckPassword(name, password))
                {
                    var identity = new GenericIdentity(name);
                    SetPrincipal(new GenericPrincipal(identity, null));
                }
                else
                {
                    // Invalid username or password.
                    HttpContext.Current.Response.StatusCode = 401;
                }
            }
            catch (FormatException)
            {
                // Credentials were not formatted correctly.
                HttpContext.Current.Response.StatusCode = 401;
            }
        }

        private static void OnApplicationAuthenticateRequest(object sender, EventArgs e)
        {
            var request = HttpContext.Current.Request;
            var authHeader = request.Headers["Authorization"];
            if (authHeader != null)
            {
                var authHeaderVal = AuthenticationHeaderValue.Parse(authHeader);

                // RFC 2617 sec 1.2, "scheme" name is case-insensitive
                if (authHeaderVal.Scheme.Equals("basic",
                        StringComparison.OrdinalIgnoreCase) &&
                    authHeaderVal.Parameter != null)
                {
                    AuthenticateUser(authHeaderVal.Parameter);
                }
            }
        }

        // If the request was unauthorized, add the WWW-Authenticate header 
        // to the response.
        private static void OnApplicationEndRequest(object sender, EventArgs e)
        {
            var response = HttpContext.Current.Response;
            if (response.StatusCode == 401)
            {
                response.Headers.Add("WWW-Authenticate",
                    string.Format("Basic realm=\"{0}\"", Realm));
            }
        }

        public void Dispose() 
        {
        }
    }
}

Step 2: Configure your new handler with IIS via your web.config.

  <system.webServer>
    <modules>
      <add name="BasicAuthHttpModule" 
        type="WebHostBasicAuth.Modules.BasicAuthHttpModule, YourAssemblyName"/>
    </modules>
  ...

Important for Excel PowerPivot

See this bug: PowerPivot not sending Authorization header in Basic Authentication to OData Svc