When a Security Token Service (STS) creates a token, that token has an absolute expiration. Usually this is about 60 minutes, after which the Relying Party (RP) has to send the user back to the STS to acquire a new token. When using Windows Identity Foundation (WIF) in ASP.NET (so for passive federation), this is the default behavior, because the SessionAuthenticationModule stores the token in the FedAuth cookie and checks that token on each request.

What’s the problem?

I hear you thinking “Cool, WIF takes care of all that for me”, and that is cool. But there’s also a nasty side effect, one which all web developers have encountered in a different context: sessions. If a user logs in, starts filling out some form, and then gets interrupted by a phone call, chances are that the session expires. This can lead to problems when the user submits the form, because the user has to log in again. The original posted data gets lost in the process, much to the frustration of the user. Because sessions use sliding expiration the problem is minor. But with absolute expiration, expiration can wreak havoc even if the user posts a form just a minute after the form was presented to the user.

Solving the problem

There are several ways to solve the problem outlined above:

1. Don’t use the SessionAuthenticationModule.
2. Modify the stored token to implement sliding expiration.
3. Force reacquiring a token in the background, so you can control when this happens.

Ditching the SessionAuthenticationModule
Not using the SessionAuthenticationModule appears to be simple. Just remove it from web.config and you’re done. However, if you remove it, you have to ensure a user stays logged in after receiving the token, and you need to keep track of the received claims. This means you need to use a cookie or session data to keep track of the user. Basically you would be recreating what the SessionAuthenticationModule does for you for free.

Making token expiration sliding
This is actually easier than ditching the SessionAuthenticationModule. All you have to do is handle the SessionSecurityTokenReceived event and modify the ValidTo property of the token, as shown in this MSDN Forums post.

Tip: You can hookup the event in the Application_Start event in global.asx using FederatedAuthentication.SessionAuthenticationModule to point to the module.

Force reacquiring a token
The above methods work fine, but have some drawbacks. One of these is the fact that Single Sign-On (SSO) no longer works properly if a user spends too long in a single application. This is because the login session with the Identity Provider will expire at some point. Another issue arises if you want to use delegation or impersonation when you call a web service. WS-Trust 1.4 supports delegation (ActAs) and impersonation (OnBehalfOf). Even though WIF officially implements WS-Trust 1.3, WIF does support these constructs. When calling web services from a web application, using delegation is a recommended practice, because it greatly improves the security. The reason is that in order for the web application to make the web service call on your behalf, it needs to acquire a token from the STS, based on the original token. This means a malicious user would need that token in order to make the web service call. Breaking into the web application is not enough.

So, how can you ensure you get a new token once in a while? Although the implementation is somewhat more difficult, the principle is simple: logout of the RP. That triggers the RP to re-authenticate the user by redirecting to the STS. As long as the user is still known in the STS, a new token is transparently given out. You can do this in roughly two ways: in an invisible iframe that does this process under the covers or in the main request stream. The latter is more visible to the user and requires you to bring the user back to where he was before the logout was forced, which is slightly more complicated than a simple redirect. The iframe solution is more elegant, because it does not interrupt the main working process. Basically all you have to do is point the iframe to a handler that logs the user out if necessary, triggering the re-authentication process when necessary and coming back to the handler to produce an empty HTML page. The handler to do this is shown in the code below.

          
            using System; using System.Configuration; using System.Globalization; using System.IdentityModel.Tokens; using System.Threading; using System.Web; using Microsoft.IdentityModel.Claims; using Microsoft.IdentityModel.Web; namespace WebApp
{ ///
<summary>///
HTTP Handler triggering token renewal when this is necessary.///
</summary>publicclass TokenRenewalHandler
: IHttpHandler { ///
<summary>///
The default number of minutes before the token expires when renewal should be triggerd.///
</summary>privateconstint DefaultTokenRenewalWindow = 20; ///
<summary>///
Value container for the TokenRenewalWindow///
</summary>privateint m_TokenRenewalWindow = 0; ///
<summary>///
Number of minutes before the token expires when renewal should be triggerd.///
</summary>///
<remarks>Should be less or equal to the session timeout.</remarks>protectedint TokenRenewalWindow
{ get { if (m_TokenRenewalWindow
== 0) { int securityTokenRenewalWindow; if (!int.TryParse(
ConfigurationManager.AppSettings["SecurityTokenRenewalWindow"],
NumberStyles.Integer, CultureInfo.InvariantCulture, out securityTokenRenewalWindow))
{ securityTokenRenewalWindow = DefaultTokenRenewalWindow;
} m_TokenRenewalWindow = securityTokenRenewalWindow;
} return m_TokenRenewalWindow;
} } ///
<summary>///
Handles the HTTP reqyest and forces a signout to renew the token if necessary.///
</summary>publicvoid ProcessRequest(HttpContext
context) { SecurityToken token =null;
IClaimsPrincipal principal = Thread.CurrentPrincipal as IClaimsPrincipal; if (principal
!=null &&
principal.Identities.Count > 0) { token = principal.Identities[0].BootstrapToken; if (token
!=null)
{ DateTime tokenExpirationTime = DateTime.Now.ToUniversalTime().AddMinutes(TokenRenewalWindow); if (token.ValidTo.ToUniversalTime().CompareTo(tokenExpirationTime)
< 0) { if (FederatedAuthentication.WSFederationAuthenticationModule
!=null)
{ //
Force sign-out. FederatedAuthentication.WSFederationAuthenticationModule.SignOut(false);
} //
Redirect to this handler to force a new sign-in request to the STS context.Response.Redirect(context.Request.RawUrl, true);
} } } //
Return an empty HTML page context.Response.ContentType ="text/html";
context.Response.Write("<html><body></body></html>");
} publicbool IsReusable
{ get { returnfalse;
} } } }
        

Bedankt allemaal voor het bezoeken van de sessie van Patriek van Dorp en mijzelf over Windows Identity Foundation op devNetNoord. Je kunt hier de slides downloaden (1,92 MB)

I am on crusade to get Windows Identity Foundation (WIF) adopted by the Microsoft .NET community at large. Why? Because maintaining a user store within an application as is propagated by ASP.NET Membership is just plain stupid these days. Yes, I may be a little harsh with that judgment, but sparing the rod spoils the child. Applications should no longer be islands, but should be working together. And if applications such as Spotify and Flickr can (re)use a user’s identity from Facebook, Twitter, LinkedIn, and so on, why can’t yours?

“A thousand mile journey begins with one step” – Lao Tze

In the past couple of years I’ve been speaking about WIF on many occasions, both at conference and with individual developers. Across the board I can say that WIF is largely misunderstood. Hence my first step is to address some of the misconceptions surrounding WIF, and more in general the concepts underlying WIF. I’ll follow up with posts showing you (to material on the web) to make it work.

Misconception 1: WIF is Microsoft-only and not interoperable.
WIF actually implements the WS-Federation standard. Microsoft is an active participant in the standards commonly known as the WS-* specifications, a host of web services specifications for security, transactions, and reliable messaging. The WS-Federation standard is implemented by many other platforms, and WIF can interoperate with these just fine.

Misconception 2: WIF can only be used to secure web applications, not web services.
The WS-Federation protocol defines two profiles: Active and Passive. Passive federation is for browser based applications, because browsers don’t support the full cryptographic stack required for WS-Federation to work. Active federation is used for web services and can be used with clients that do support the needed cryptographic capabilities. I’ll get back to what this all means in another post.

Misconception 3: WIF can only be used to secure web services, not web applications.
See misconception #2.

Misconception 4: WIF is only for cloud (Azure) applications.
WIF works with any application written in .NET 3.5 and up. You can host that application anywhere you like, in the cloud or in your own data center. In fact, there is nothing that prevents you from creating applications with WIF for use in just the local network and for internal use only.

Misconception 5: You can’t do role-based security with WIF.
Quite the opposite is true. You can still do role-based security if you want to, but you can do much more. The underlying protocol is much more flexible, and you can implement security checks in your applications based on the information you get about a use any way you like.

Misconception 6: WIF only adds complexity.
It is indeed true that properly connecting a WIF enabled application to a security token service can be a challenge. You need to get the protocol settings to match and need certificates for encryption and signing. However, inside your applications WIF is just as easy as role-based security as you are used to. If you want to do more elaborate things, things obviously get more complex, but this is true for any type of security.

Misconception 7: To use WIF in an existing application I need to re-architect the whole application.
WIF extends the IIdentity and IPrincipal interfaces. This means that your existing application will keep working if you migrate to WIF to get authenticate and authorize the user. The only thing you need to be aware of is the fact that because you don’t have a local user directory anymore, you can’t do things for which you require information about another user. This means you may have to provide a different way to deal with such scenarios. If you use ASP.NET Profiles for this kind of information, a custom provider may be all you need.

Op 15 februari vanaf 18u15 geeft Beth Massi een gratis Masterclass Visual Studio LightSwitch. Wees er snel bij, want je kunt je tot 10 februari inschrijven en er is een beperkt aantal plaatsen. Zie de uitnodiging hieronder voor meer informatie.

Programming Amazon EC2 by Jurg van Vliet and Flavia Paganelli is practical in nature and takes you through all the steps to create and configure accounts, develop applications, and deploy applications. If you’re new to Amazon EC2 (and related services) this is definitely a good place to start, because it goes through all the components Amazon offers, such as S3/Cloudfront and RDS for data storage. It also looks at how you can setup your application to scale up and down, and ensure your application has excellent uptime. The book takes you by the hand based on some applications the authors have created themselves. Although this approach makes the book practical, it sometimes reads as (irritating) marketing for their applications.

Workflow Services in .NET 4 allow you to do long running processes. But when you do that, there's an interesting question: when a workflow has been suspended, under which user is the workflow running when it is active again. To answer this question I created a simple workflow that writes the user in the current thread to a log. On the initial call, the user making the call was logged (in this case I used Windows Identity Foundation to authenticate, but this should be the same for all types of authentication). After a Delay of a minute that user was gone, and instead the user in the current thread was unauthenticated. This means that any code you call from the workflow can't rely on Thread.CurrentPrincipal to get the proper authorizations. You have to save the user, and somehow reinstate principal so it runs under the original context. Alternatively you can use some form of delegation.

Working with Windows Idnentity Foundation can be quite a minefield. Solve one issue, and the next creeps up. Because it's all these little tweaks to make it work, I often find myself thinking "How did I solve that last time?" One of those issues is the exception

Could not establish trust relationship for the SSL/TLS secure channel with authority 'somesite.runningunder.ssl'

There are two reasons why you can run into this exception, each discussed below.

The certificate isn't trusted and/or the URL doesn't correspond with the URL in the certificate. If this is the case, you get certificate warnings when you browse to the service WSDL with a browser. The best way to solve the former is to have your (development) environment work with certificates it trusts. This means setting up a Certificate Authority (Active Directory Certificate Services), placing the root CA certificate in the Trusted Root Certificates of the machine your clients (and services) run on, issuing the needed certificates from the CA, and placing these where they are needed. Alternatively, you can just add a single line of code to your client so it ignores certificate issues before you do any service call:

System.Net.ServicePointManager.ServerCertificateValidationCallback =
    ((sender, certificate, chain, sslPolicyErrors) => true);

WARNING! ONLY USE THE ABOVE CODE FOR DEVELOPMENT PURPOSES. IT IS NOT SECURE.

If after you've done the above you still get an exception, the above code is likely not even being hit. That means you (also) have the problem below.

You've setup identity trust in your client, and the certificate reference is incorrect. This often happens when you copied some configuration from somewhere, and forgot to change the corresponding certificate reference. The red stuff in the client configuration below (which is much longer in a real configuration) is the culprit. It should contain the encoded certificate.

          <system.serviceModel>
<client> <endpoint address="https://YourServer/Service1.svc" binding="customBinding"
bindingConfiguration="CustomBinding_IService1" contract="ServiceReference1.IService1"
name="Service1Binding"> <identity> <certificate encodedValue="MIIF5jCCBM6gAwIBAgIKYSt2tQA..."/>
</identity> </endpoint> </client> </system.serviceModel>
        

To solve this, you need to get the base64 encoded certificate string, and paste it in place of what's in there now. To get it you can do the following:

1. Browse to the endpoint with your browser.
2. View the certificate information.
3. Save the certificate to file.
4. Open the certificate with notepad.
5. Copy the encoded value between the -----BEGIN CERTIFICATE----- and -----END CERTIFICATE----- placeholders.
   

I've been working with WCF for quite a while, and every so often I run into this exception:

ArgumentException: The provided URI scheme 'https' is invalid; expected 'http'.Parameter name: via

The problem is obvious. You're trying to access a service under HTTPS, but it's being called with HTTP. Under most bindings you can solve this by adding somehting like this to the client binding configuration:

<binding name="MyBinding"> 
  <security mode="Transport">
<transport clientCredentialType="None" /> <message clientCredentialType="None"
negotiateServiceCredential="false" establishSecurityContext="false" /> </security>
</binding>

When you use a (custom) ws2007FederationHttp binding, for instance when working with Windows Identity Foundation, the above won't work. In that case you need to look in the binding for the <httpTransport> element and replace it with <httpsTransport>.

Recently I had the pleasure of diving into audit logging. I’m working on a government project which involves the law making process, so it is imperative that all database changes are completely traceable. That means that we need to be able to trace who made which changes and when. We’re working with latest and greatest version of SQL Server (i.e. SQL Server 2008 R2), which has a feature called SQL Audit. Reading the documentation SQL Audit seemed to do everything we need, except that it doesn’t know which application user is making the changes. This is logical since it is a web application and we’re using delegation. For this reason we were already planning to have the application send along the user id when it does an insert, update or delete, and we decided to only logically delete a record. So far so good.

When it came to testing, we quickly found that SQL Audit logs the SQL statement making the change. Sounds right doesn’t it? Well actually it isn’t. LINQ-to-SQL, LINQ-to-Entities and other O/R Mappers use parameter queries, and in fact if you edit records in the SQL Management Studio UI, the same is true. The problem is that the parameters are not part of the SQL statement being logged! So we can see which database user made what kind of change, but not which data was changed, and hence not which application user made the change either. Back to the drawing board :(.

In reviewing our options, we looked at:

• All logging in the O/R Mapper: Not an option, because we need to know what DBA’s do too.
• SQL Trace: not recommended by Redmond, and it takes a huge performance hit.
• Triggers: in transaction, taking enormous performance hit.
• C2 auditing: tracks all changes, so it gathers huge amounts of data, not easily searchable.
• Change Data Capture: really for BI purposes, deleted after three days, no indication of the user making the change.

All of the above options have some sort of problem associated with it. The conclusion is that there is no single solution, unless Microsoft fixes the SQL Audit issue (you can vote on it here: https://connect.microsoft.com/SQLServer/feedback/details/624935/sql-server-2008-database-audit-on-insert-update-and-delete-actual-sql-and-not-parameter-values).

We now do the following:

1. In the Data Access Layer add the application user that did the insert or update in an extra field on the table.
2. Only do logical deletes (i.e. add a “Deleted” flag to a table).
3. Track all changes using Change Data Capture (which uses the transaction log and therefore has less impact on performance).
4. Export CDC data to an “Audit Database” periodically (like using a data warehouse).
5. Use SQL Audit for all changes done by a database user other than the DB account used by the application.
6. Export SQL Audit logs to the Audit Database periodically.

By cross referencing SQL Audit and CDC data, we can figure out who changed what if the change was made outside the application.

I just upgraded my blog to the latest version of dasBlog. I also moved to another hosting provider. All content has been migrated, but there may be links that are not working on very old posts. I'll check these in the coming days so everything works as it should. If you happen to run ito problems, let me know.