Custom WIF Request Validator Infinite Loop

Question

While fixing the problem described here, I created another that I can seem to find anywhere else on the web:

SignInResponseMessage message = WSFederationMessage.CreateFromFormPost(context.Request) as SignInResponseMessage;

The above code keeps calling IsValidRequestString() which causes an infinite loop. The call is the same each time and the stack looks like this:

>   TestIdentityBroker.dll!TestIdentityBroker.Service.WsFederationRequestValidator.IsValidRequestString(System.Web.HttpContext context, string value, System.Web.Util.RequestValidationSource requestValidationSource, string collectionKey, out int validationFailureIndex) Line 19    C#
[External Code] 
TestIdentityBroker.dll!TestIdentityBroker.Service.WsFederationRequestValidator.IsValidRequestString(System.Web.HttpContext context, string value, System.Web.Util.RequestValidationSource requestValidationSource, string collectionKey, out int validationFailureIndex) Line 19 + 0x21 bytes   C#
[External Code] 
TestIdentityBroker.dll!TestIdentityBroker.Service.WsFederationRequestValidator.IsValidRequestString(System.Web.HttpContext context, string value, System.Web.Util.RequestValidationSource requestValidationSource, string collectionKey, out int validationFailureIndex) Line 19 + 0x21 bytes   C#
[External Code] 
TestIdentityBroker.dll!TestIdentityBroker.Service.WsFederationRequestValidator.IsValidRequestString(System.Web.HttpContext context, string value, System.Web.Util.RequestValidationSource requestValidationSource, string collectionKey, out int validationFailureIndex) Line 19 + 0x21 bytes   C#
[External Code] 

This is happening in a custom relying party security token service that federates identity from my relying party to an ip created by the FedUtil tool. Does anyone know why WSFederationMessage.CreateFromFormPost() would call the request validator? The returned wreply seems normal.

EDIT: This only happens when I have already been authenticated once before. If I clear my browser cache it doesn't happen.

<?xml version="1.0"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=152368
  -->
<configuration>
  <configSections>
    <section name="microsoft.identityModel" type="Microsoft.IdentityModel.Configuration.MicrosoftIdentityModelSection, Microsoft.IdentityModel, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
  </configSections>
  <connectionStrings>
    <add name="ApplicationServices" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true" providerName="System.Data.SqlClient" />
  </connectionStrings>
  <appSettings>
    <add key="webpages:Version" value="1.0.0.0" />
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />
    <add key="FederationMetadataLocation" value="X:\WebTest\TestIdentityBroker\TestIdentityBroker_STS\FederationMetadata\2007-06\FederationMetadata.xml" />
    <add key="SigningCertificateName" value="CN=Dev4"/>
  </appSettings>
  <location path="FederationMetadata">
    <system.web>
      <authorization>
        <allow users="*" />
      </authorization>
    </system.web>
  </location>
  <system.web>
    <!--<authorization>
      <deny users="?" />
    </authorization>-->
    <compilation debug="true" targetFramework="4.0">
      <assemblies>
        <add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        <add assembly="System.Web.Helpers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        <add assembly="System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        <add assembly="System.Web.WebPages, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        <add assembly="Microsoft.IdentityModel, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
      </assemblies>
    </compilation>
    <!--<authentication mode="Forms">
      <forms loginUrl="~/Federation/Authenticate" timeout="2880" />
    </authentication>-->
    <authentication mode="None" />
    <membership>
      <providers>
        <clear />
        <add name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServices" enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false" maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10" applicationName="/" />
      </providers>
    </membership>
    <profile>
      <providers>
        <clear />
        <add name="AspNetSqlProfileProvider" type="System.Web.Profile.SqlProfileProvider" connectionStringName="ApplicationServices" applicationName="/" />
      </providers>
    </profile>
    <roleManager enabled="false">
      <providers>
        <clear />
        <add name="AspNetSqlRoleProvider" type="System.Web.Security.SqlRoleProvider" connectionStringName="ApplicationServices" applicationName="/" />
        <add name="AspNetWindowsTokenRoleProvider" type="System.Web.Security.WindowsTokenRoleProvider" applicationName="/" />
      </providers>
    </roleManager>
    <pages>
      <namespaces>
        <add namespace="System.Web.Helpers" />
        <add namespace="System.Web.Mvc" />
        <add namespace="System.Web.Mvc.Ajax" />
        <add namespace="System.Web.Mvc.Html" />
        <add namespace="System.Web.Routing" />
        <add namespace="System.Web.WebPages" />
      </namespaces>
    </pages>
    <httpRuntime requestValidationType="TestIdentityBroker.Service.WsFederationRequestValidator" />
    <httpModules>
      <add name="WSFederationAuthenticationModule" type="Microsoft.IdentityModel.Web.WSFederationAuthenticationModule, Microsoft.IdentityModel, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      <add name="SessionAuthenticationModule" type="Microsoft.IdentityModel.Web.SessionAuthenticationModule, Microsoft.IdentityModel, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      <add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, System.Web.Routing, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
    </httpModules>
  </system.web>
  <system.webServer>
    <validation validateIntegratedModeConfiguration="false" />
    <modules runAllManagedModulesForAllRequests="true">
      <add name="WSFederationAuthenticationModule" type="Microsoft.IdentityModel.Web.WSFederationAuthenticationModule, Microsoft.IdentityModel, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" preCondition="managedHandler" />
      <add name="SessionAuthenticationModule" type="Microsoft.IdentityModel.Web.SessionAuthenticationModule, Microsoft.IdentityModel, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" preCondition="managedHandler" />
    </modules>
  </system.webServer>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="3.0.0.0" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
  <microsoft.identityModel>
    <service>
      <audienceUris>
        <add value="https://rp_sts.local/" />
        <add value="https://rp_sts.local/Federation/LogOn" />
      </audienceUris>
      <federatedAuthentication>
        <wsFederation passiveRedirectEnabled="false" issuer="https://ip.local/" realm="https://rp_sts.local/" requireHttps="false" />
        <cookieHandler requireSsl="true" />
      </federatedAuthentication>
      <applicationService>
        <claimTypeRequired>
          <!--Following are the claims offered by STS 'http://ip.local/'. Add or uncomment claims that you require by your application and then update the federation metadata of this application.-->
          <claimType type="http://schemas.xmlsoap.org/ws/2005/05/identity/claims/name" optional="true" />
          <claimType type="http://schemas.microsoft.com/ws/2008/06/identity/claims/role" optional="true" />
        </claimTypeRequired>
      </applicationService>
      <issuerNameRegistry type="Microsoft.IdentityModel.Tokens.ConfigurationBasedIssuerNameRegistry, Microsoft.IdentityModel, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
        <trustedIssuers>
          <add thumbprint="xx" name="https://ip.local/" />
        </trustedIssuers>
      </issuerNameRegistry>
    </service>
  </microsoft.identityModel>
</configuration>

Answer 1

The problem is that when a user is authenticated, accessing System.HttpContext.Current.Request at all triggers the RequestValidator to be executed.

So passing a System.HttpContext.Current.Request reference into WSFederationMessage.CreateFromFormPost inside the RequestValidator initiates the infinite loop. I have not looked into why this problem occurs.

While you could decide to not process requests for users already authenticated at your STS (as you did), that doesn't work if your code is an intermediate STS that relies on another issuer. For example, if the requesting RP passes a different WHR you would still want to reprocess up to your parent STS in case the different home realm issues different claims.

In my case I was forced to modify my request validator by simply returning true if there is a wresult parameter present. By doing so, responsibility to validate the incomming message is delegated to the code that processes signin requests:

public class WIFRequestValidator : RequestValidator
{
    protected override bool IsValidRequestString(HttpContext context, string value, RequestValidationSource requestValidationSource, string collectionKey, out int validationFailureIndex)
    {
        validationFailureIndex = 0;

        if (requestValidationSource == RequestValidationSource.Form && collectionKey.Equals(WSFederationConstants.Parameters.Result, StringComparison.Ordinal))
        {
            return true;

            //SignInResponseMessage message = WSFederationMessage.CreateFromFormPost(context.Request) as SignInResponseMessage;
            //if (message != null)
            //{
                //return true;
            //}
        }

        return base.IsValidRequestString(context, value, requestValidationSource, collectionKey, out validationFailureIndex);
    }
}   

Answer 2

The original Technet wiki page now contains fixed version of the code. The solution is to explicitly skip validation while getting the collection of POST data.

var unvalidatedFormValues = System.Web.Helpers.Validation.Unvalidated(context.Request).Form;
SignInResponseMessage message = WSFederationMessage.CreateFromNameValueCollection( WSFederationMessage.GetBaseUrl( context.Request.Url ), unvalidatedFormValues ) as SignInResponseMessage;

The Validation class belongs to the System.Web.WebPages.dll assembly, which is usually installed along with ASP.NET MVC.

I did not want to bind my utility library to MVC, so I looked into the Validation class with a decompiler and used a lower-level method from the Microsoft.Web.Infrastructure.dll which I already had referenced:

var baseUrl = WSFederationMessage.GetBaseUrl(context.Request.Url);
Func<NameValueCollection> formGetter, queryStringGetter;
Microsoft.Web.Infrastructure.DynamicValidationHelper.ValidationUtility.GetUnvalidatedCollections(context, out formGetter, out queryStringGetter);
if (WSFederationMessage.CreateFromNameValueCollection(baseUrl, formGetter()) is SignInResponseMessage)
    return true;