NullReferenceException on Bootstraptoken (ACS authentication) - windows-8

Question

I've been following the steps to make a Windows 8 Store app get an ACS token as described here:
Does the WebAuthenticationBroker work in Windows 8 Metro App post Release Candidate
Authentication method of Windows 8 client
private async void Authenticate()
{
WebAuthenticationResult webAuthenticationResult = await WebAuthenticationBroker.AuthenticateAsync(
WebAuthenticationOptions.None,
new Uri("https://myACSnamespace.accesscontrol.windows.net:443/v2/wsfederation?wa=wsignin1.0&wtrealm=http://localhost:12714/"),
new Uri("http://mypublicIPaddress:80/WebAppMVCAPI/api/federation/end"));
My controller on the web application is programmed as follows:
public class FederationController : ApiController
{
protected virtual string ExtractBootstrapToken()
{
return HttpContext.Current.User.BootstrapToken();
}
[HttpGet]
public string Get()
{
return "Hello Get World";
}
[HttpPost]
public HttpResponseMessage Post()
{
var response = this.Request.CreateResponse(HttpStatusCode.Redirect);
response.Headers.Add("Location", "/WebAppMVCAPI/api/federation/end?acsToken=" + ExtractBootstrapToken());
return response;
}
}
}
The idea is to have the Windows 8 store app get a token from ACS with a Facebook login. When I launch the win8 client, the application shows a Facebook login page. However, the instruction return HttpContext.Current.User.Bootstraptoken() fails with the following exception:
NullReferenceException. Object reference not set to an instance of an object.
My web.config looks like this:
<microsoft.identityModel>
<service saveBootstrapTokens="true">
<audienceUris>
<add value="http://localhost:80" />
</audienceUris>
<federatedAuthentication>
<wsFederation passiveRedirectEnabled="true" issuer="https://bondsapp.accesscontrol.windows.net/v2/wsfederation" realm="http://localhost:80/" reply="http://localhost:80/" requireHttps="false" />
<cookieHandler requireSsl="false" path="/" />
</federatedAuthentication>
<issuerNameRegistry type="Microsoft.IdentityModel.Swt.SwtIssuerNameRegistry, Wif.Swt">
<trustedIssuers>
<add name="https://bondsapp.accesscontrol.windows.net/" thumbprint="xxxxx" />
</trustedIssuers>
</issuerNameRegistry>
<securityTokenHandlers>
<add type="Microsoft.IdentityModel.Swt.SwtSecurityTokenHandler, Wif.Swt" />
</securityTokenHandlers>
<issuerTokenResolver type="Microsoft.IdentityModel.Swt.SwtIssuerTokenResolver, Wif.Swt" />
</service>
Can somebody shed some light on how to use the Bootstraptoken method to get an ACS token?
Thanks
Luis

Answer 1

I don't believe that federated authentication sets HttpContext.User by default. Try
(Thread.CurrentPrincipal as IClaimsPrincipal).Identities[0].BootstrapToken
Assuming that you've gone through the token handler pipeline (WS-FAM) at your site, this should be populated. This will be a SecurityToken object, which you can then serialize using the proper SecurityTokenHandler class.

Answer 2

Did you try this :
BootstrapContext bootstrapContext = ClaimsPrincipal.Current.Identities.First().BootstrapContext as BootstrapContext;
SecurityToken st = bootstrapContext.SecurityToken;
Take a look on Vittorio's post:
http://blogs.msdn.com/b/vbertocci/archive/2012/11/30/using-the-bootstrapcontext-property-in-net-4-5.aspx