Tag Archives: AD FS

May 16, 2013 · 7:27 pm

13 Shades of Claims Based Authentication

With this post I’m going to kick off a series of posts that will cover different topologies in which claims based authentication can be used. We are all familiar with the classic model where the client accesses the application and get redirected to the STS for obtaining the security token. The simplest configuration would have this STS to act both as Resource Provider STS and Identity Provider STS. The next is classic configuration with federation with trusted Identity provider organization. There are many more options on how it all can be configured, all really depends on the specific customer requirements. So I want to try and explorer multiple topologies and record a short demonstration for each of them so you can see what is possible and potentially how it can be done.

Here is what I have currently in mind:

  1. Client – Application – RP – IDP
  2. Client – Application – RP – RP – IDP
  3. Client – Application – RP – RP – RP – IDP
  4. Introduce Proxy components in the above topologies
  5. Introduce multiple IDPs in the above topologies
  6. Introduce different authentication mechanisms in the above topologies (Integrated, FBA, Certificate, PhoneFactor)
  7. Introduce mechanisms to provide automated HRD discovery
  8. Introduce IDP initiated sign on
  9. Introduce UAG as reverse proxy in the middle
  10. Introduce Azure Active Directory as IDP
  11. Introduce Azure ACS as middle tier to get authentication via Social identities (Microsoft, Facebook, Yahoo, Google)

As I work on these scenarios I might drop some of them and I might decide to explorer some other topologies that I have not thought about yet. If you have ideas of what would be interesting to explore then let me know and I might try to get it on my agenda.

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August 18, 2012 · 11:33 am

Chaining Multiple STS

A few month ago I learned something about claims based authentication that I thought was not possible.

Ever since starting working on federation solutions, and learning about it via training courses, reading white papers, specifications and presentations the following two topologies were always shown or discussed. The first one is where company has its own STS and their applications configured with this STS. The second solution extends on the first one by federation between two STSs, where one STS is acting as RP and the second is acting as IdP. I have never seen any specs or designs that would show more than two STSs in a chain, ie something like this RP-RP-IdP. So for some time I was assuming that protocols that make it all happen (WS-Fed, SAML etc) are designed to work in specific model RP-IdP and would not go beyond this one-one relationship. While this works for majority of the real world situations, in some cases it does not satisfy the complex requirements where chaining of the multiple STSs is required. Well, I thought that it was not possible till a few month ago. I had to design complex federation architecture and this perceived limitation was giving me a lot of headache. So, obviously I did some research and talked to a few people who also specializes in federation solutions and to my great surprise I learned that there is no limitation with protocols and that it is just fine to setup multiple STSs in a chain of trusts. I wish that I learned it prior from someone else’s design or spec paper, clearly stating that it is fine to do this and it will work. Needless to say, we were able to configure our architecture and satisfy customer requirements without additional overhead and keep it very streamlined.

A few days ago I was rebuilding my lab and decided to configure it to illustrate chaining of multiple STSs and show it here. So if anyone else didn’t decipher it in spec papers or other design, and is thinking that chaining is not possible, that it is in fact possible and works just fine. You can use it in your designs if it is a requirement.

In my lab I configured the following to illustrate this configuration:

  • IdP STS (DC, AD FS 2.0), it has the following FS URL: fs1.contoso.com
  • RP STS (AD FS 2.0), this is a middle STS, with FS URL: fs2.contoso.com
  • RP STS (AD FS 2.0), this is the STS with target relying party application. FS URL: fs1.external.com
  • Relying Party (Sample WIF SDK app). This is a workgroup server configured with fs1.external.com as its STS. Application URL https://myclaims.external.com/myclaims
  • Workstation that will access the application. I have HTTPWatch installed on this PC to show all traffic passive request traffic between the browser and the target systems.

Figure 1 shows my lab configuration:

Figure 1

Figure 1: Chaining multiple STS

Figure 2 shows the HTTPWatch traffic captured on the client PC. As you can see in steps 1 to 10, the browser steps through all parties in the authentication process and authenticates me into the application. It is fairly self explanatory, but if you have questions then let me know if you need any explanation on what happens here.

image

Figure 2: HTTPWatch capture of the Passive Request traffic with multiple chained STS (click on it to see it large)

Finally, you might ask why would anyone need to chain STS in such way. To answer it I’ll have to write another blog post. So stay tuned, I might do that in the next month or so.

Thanks, Dmitrii

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June 27, 2012 · 1:52 pm

Authentication Assurance and Claims Based Authentication

Authentication Mechanism Assurance is described in the following Microsoft publication: http://technet.microsoft.com/en-us/library/dd378897(v=WS.10).aspx.

In this post I want to dig a bit more into different configuration options, show how it works and provide example of how it can be configured with AD FS 2.

Authentication Mechanism Assurance is a new feature in Windows 2008 R2 AD DS configured at 2008 R2 Functional level, it provides an ability to assure that user is authenticated with specific type of certificate. Usually it is used to assure that user is authenticated with a specific type of smart card into AD DS. This assurance can then be passed on to applications which will make authorization decision on what user can or cannot do in it. It is very important feature in environments where specific regulations require to provide assurance of Smart Card authentication.

AD DS configured to use Authentication Mechanism Assurance is capable to identify users who used specific type of Smart Cards for authentication and dynamically populate their Kerberos tickets with security group associated with those specific Smart Cards. The linkage between Smart Card and AD DS is done via the OID populated in Certificate Policy certificate extension. Let’s take a quick look at how it works. The following diagram shows a basic flow of authentication to claims based application which can take advantage of the authentication assurance claim. In our example Contoso has Smart Cards with X.X.XX.XXX.X.X.X.X OID populated in Certificate Policy certificate extension. AD DS is configured to link X.X.XX.XXX.X.X.X.X OID with “Smart Card X Authenticated” security group.

In step 1, user authenticates to their desktop by providing Smart Card and PIN number. During authentication process AD DS detects that user authenticates with Smart Card (it is done by finding X.X.XX.XXX.X.X.X.X OID in the user certs) and builds Kerberos ticket. AD DS will include “Smart Card X Authenticated” security group SID in the Kerberos ticket.

In step 2, user tries to access claims based application which will redirect the browser to its trusted STS.

In step 3 and 4 user will be authenticated to the STS. STS will examine user group membership and because user’s Kerberos ticket contains “Smart Card X Authenticated” SID it will issue special claim type indicating that user was authenticated to AD DS with their Smart Card.

This token will be passed to the application. In step 5, application will have a choice to provide different logic for users who authenticated to AD DS with a Smart Card or without. Simple enough.

 AuthNMechanismAssurance

Let’s take a look how it all can be configured. I’m not going to repeat some of the steps described in the before mentioned Microsoft publication. I’ll refer to it when necessary.

The first step in configuring Authentication Mechanism Assurance is to create proper Issuance Policy in AD DS. The OID in AD DS Issuance Policy must match the OID in Certificate Policy on the Authentication certificate on the Smart Card. It will look something like this on the certificate:

[1]Certificate Policy:

Policy Identifier=X.XX.XXX.X.XXX.X.X.X.X.XX

More likely your AD DS will not have this OID and you’ll need to create one. Fortunately it is easy to do:

  1. Open Certificate Template management console.
  2. Open any v2 certificate template.
  3. Click on Extensions Tab, Click on “Issuance Policies” and then click Edit.
  4. Click on Add, then click on New.
  5. In the Name field type: Smart Card AuthN Cert
  6. In the object identifier field type: X.XX.XXX.X.XXX.X.X.X.X.XX (where XXX – is the OID from the cert on Smart Card)
  7. Click OK
  8. Do not save changes to the certificate template. Exit Certificate Management Console.

At this point you are ready to link appropriate security group to the Certificate Issuance policy. Create get-IssuancePolicy.ps1 and set-IssuancePolicyToGroupLink.ps1 files as described in Microsoft article. Run the first one to see if there are policies already in place. Run the second to make the linkage.

To display run this: .\get-IssuancePolicy.ps1 –LinkedToGroup:All

To create new policy: .\set-IssuancePolicyToGroupLink.ps1 –IssuancePolicyName “Smart Card AuthN Cert” –groupOU “Auth Mech Assurance” –groupName “Smart Card Authenticated”

To see new policy: .\get-IssuancePolicy.ps1 –LinkedToGroup:All

So far, so good. We configured Authentication Mechanism Assurance. To verify that it actually working logon to AD DS with Smart Card, open command prompt and type whoami /groups. It will list all the groups that you belong, one of them will be Smart Card Authenticated. Logon with UserID/pwd and you’ll not be member of that group.

The next step is really making some use out of this information. Applications must be designed to take advantage of this information and make authorization decisions based on level of assurance we provide to it. Perfect candidates for it are claims based applications. We can generate a claim type, for example lets name it “LOA”, which stands for Level of Assurance, and assign different value to it. If user used userID/pwd, we assign 2 to LOA, if user used Smart Card then LOA will have 3. Application will decide what to do base on those values in LOA claim type.

Next, we are going to create LOA claim type in AD FS 2 and pass it to the application. I’ll discuss it in the next post.

Thanks for stopping by.

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· 1:31 pm

Authentication Assurance and Claims Based Authentication

Authentication Mechanism Assurance is described in the following Microsoft publication: http://technet.microsoft.com/en-us/library/dd378897(v=WS.10).aspx.

In this post I want to dig a bit more into different configuration options, show how it works and provide example of how it can be configured with AD FS 2.

Authentication Mechanism Assurance is a new feature in Windows 2008 R2 AD DS configured at 2008 R2 Functional level, it provides an ability to assure that user is authenticated with specific type of certificate. Usually it is used to assure that user is authenticated with a specific type of smart card into AD DS. This assurance can then be passed on to applications which will make authorization decision on what user can or cannot do in it. It is very important feature in environments where specific regulations require to provide assurance of Smart Card authentication.

AD DS configured to use Authentication Mechanism Assurance is capable to identify users who used specific type of Smart Cards for authentication and dynamically populate their Kerberos tickets with security group associated with those specific Smart Cards. The linkage between Smart Card and AD DS is done via the OID populated in Certificate Policy certificate extension. Let’s take a quick look at how it works. The following diagram shows a basic flow of authentication to claims based application which can take advantage of the authentication assurance claim. In our example Contoso has Smart Cards with X.X.XX.XXX.X.X.X.X OID populated in Certificate Policy certificate extension. AD DS is configured to link X.X.XX.XXX.X.X.X.X OID with “Smart Card X Authenticated” security group.

In step 1, user authenticates to their desktop by providing Smart Card and PIN number. During authentication process AD DS detects that user authenticates with Smart Card (it is done by finding X.X.XX.XXX.X.X.X.X OID in the user certs) and builds Kerberos ticket. AD DS will include “Smart Card X Authenticated” security group SID in the Kerberos ticket.

In step 2, user tries to access claims based application which will redirect the browser to its trusted STS.

In step 3 and 4 user will be authenticated to the STS. STS will examine user group membership and because user’s Kerberos ticket contains “Smart Card X Authenticated” SID it will issue special claim type indicating that user was authenticated to AD DS with their Smart Card.

This token will be passed to the application. In step 5, application will have a choice to provide different logic for users who authenticated to AD DS with a Smart Card or without. Simple enough.

Let’s take a look how it all can be configured. I’m not going to repeat some of the steps described in the before mentioned Microsoft publication. I’ll refer to it when necessary.

The first step in configuring Authentication Mechanism Assurance is to create proper Issuance Policy in AD DS. The OID in AD DS Issuance Policy must match the OID in Certificate Policy on the Authentication certificate on the Smart Card. It will look something like this on the certificate:

[1]Certificate Policy:

Policy Identifier=X.XX.XXX.X.XXX.X.X.X.X.XX

More likely your AD DS will not have this OID and you’ll need to create one. Fortunately it is easy to do:

  1. Open Certificate Template management console.
  2. Open any v2 certificate template.
  3. Click on Extensions Tab, Click on “Issuance Policies” and then click Edit.
  4. Click on Add, then click on New.
  5. In the Name field type: Smart Card AuthN Cert
  6. In the object identifier field type: X.XX.XXX.X.XXX.X.X.X.X.XX (where XXX – is the OID from the cert on Smart Card)
  7. Click OK
  8. Do not save changes to the certificate template. Exit Certificate Management Console.

At this point you are ready to link appropriate security group to the Certificate Issuance policy. Create get-IssuancePolicy.ps1 and set-IssuancePolicyToGroupLink.ps1 files as described in Microsoft article. Run the first one to see if there are policies already in place. Run the second to make the linkage.

To display run this: .\get-IssuancePolicy.ps1 –LinkedToGroup:All

To create new policy: .\set-IssuancePolicyToGroupLink.ps1 –IssuancePolicyName “Smart Card AuthN Cert” –groupOU “Auth Mech Assurance” –groupName “Smart Card Authenticated”

To see new policy: .\get-IssuancePolicy.ps1 –LinkedToGroup:All

So far, so good. We configured Authentication Mechanism Assurance. To verify that it actually working logon to AD DS with Smart Card, open command prompt and type whoami /groups. It will list all the groups that you belong, one of them will be Smart Card Authenticated. Logon with UserID/pwd and you’ll not be member of that group.

The next step is really making some use out of this information. Applications must be designed to take advantage of this information and make authorization decisions based on level of assurance we provide to it. Perfect candidates for it are claims based applications. We can generate a claim type, for example lets name it “LOA”, which stands for Level of Assurance, and assign different value to it. If user used userID/pwd, we assign 2 to LOA, if user used Smart Card then LOA will have 3. Application will decide what to do base on those values in LOA claim type.

Next, we are going to create LOA claim type in AD FS 2 and pass it to the application. I’ll discuss it in the next post.

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October 29, 2011 · 10:57 am

AD FS and UAG are Better Together–Example of a real Solution

In the last nine posts we reviewed different topologies and discussed some of the techniques on how to integrate these topologies together. In this post we’ll take a look at real example of a production implementation.

The solution very similar to the following design has been implemented by one of the large enterprise companies. We will review it here in some detail. Every real world implementation is based on some type of specific requirements that the customer would like to satisfy. The solution is called “Application Gateway” or simply “Gateway”. The following are the main requirements that this solution must satisfy:

  • Provide a secure infrastructure solution that can be accessed by users over the Internet.
  • Provide an application portal to host applications for access by both internal and external users.
  • Allow external users to create accounts.
  • Allow external users to change their passwords.
  • Provide external users with self-service password reset functionality.
  • Allow internal users to leverage their current existing credentials for gaining access to the resources in this solution.
  • Federated access to published applications by partner users.
  • The solution must be secure, implemented in the DMZ environment, and ideally without Windows trusts between this solution environment and internal AD.

I just listed the main ones, but there are many more specific requirements. Those are not necessarily dictating the overall solution architecture.

The following software components are part of the solution, with Figure 1 showing how they relate to each other:

  • FIM 2010 R2 – All IDM related functions
    • Self-registration for external users
    • SSPR for external users
    • Group Management for application access AuthZ
    • Approval Workflows for user creation
  • UAG SP1 – External and Internal entry into the application hosting environment
  • AD FS v2 – Authentication into the environment
    • For external users access to SAML apps
    • For internal users SSO to Gateway and access to SAML Apps
  • SCOM/ACS – Monitoring and Audit
  • AD – Directory Services

image

Figure 1: Solution Components

UAG Trunk Design in this solution will have at least three trunks on each UAG server, as shown in Figure 2.

  1. The first trunk will publish Anonymous applications. This trunk will be configured without any authentication requirements. The following are primary applications that will be published via this trunk:
    1. Initial landing page for users with menu selection of different tasks
    2. Self Service Password Reset application
    3. Self-User Registration application
  2. The second trunk will publish a portal for external users with password change function
    1. This trunk will use AD for primary authentication to the portal
    2. Will use AD FS as secondary for claims-enabled apps
  3. The third trunk will publish a portal for users authenticating via SAML (Federated)
    1. This trunk will use AD FS as the primary authentication to the portal
    2. It will be configured as a relaying party with RP-STS

image

Figure 2: UAG Trunks

Figure 3 shows Federation configuration for this solution. It will have at least three AD FS Farms:

  1. The first farm will act as resource provider, and it will be configured with all applications in the Gateway application environment. All claims-enabled applications will trust this STS. In Figure 23, it is shown as RP-STS (fs2.fabrikam.com). As you can see, both UAG servers, specifically ADFS configured trunks, are some of the applications that are configured as relying parties with this RP-STS.
  2. The second AD FS server farm will provide SAML tokens to external users with accounts in the Gateway Active Directory. It will act as an identity provider to external users who have accounts in the Gateway AD. This STS is shown as IdP-STS (fs1.fabrikam.com). This STS will not be accessed via UAG as by means of UAG proxy. Instead it will be published on the FBA trunk as a secondary authentication provider.
  3. The third AD FS server farm will provide SAML tokens to internal users with accounts in Corporate Fabrikam AD. It will act as an identity provider to internal users. This STS is shown as IdP-STS (fs3.fabrikam.com). This STS is not published via UAG. In fact, it is providing Federated WebSSO to the RP-STS, so that internal Fabrikam users will be able to authenticate into the Gateway environment without being required to have a known UserID/Password in the Gateway AD.

image

Figure 3: Federation Design

At this point, we need to review a very important technical requirement that must be satisfied for this solution to work. Internet facing UAG and internally exposed UAG must be resolved via the same DNS name. They must be identical. In other words, if an Internet based client types in the browser the name for this portal as portal.fabrikam.com, it should resolve to the external UAG IP address. At the same time, if internal user, using a computer on the corporate network is using the same URL, it should be resolved to the internal UAG server IP address. Why is this the case? It actually has nothing to do with UAG. This requirement comes from AD FS – the federation service URL always stays the same. In our example, if the client needs to get a SAML token from the fs2.fabrikam.com AD FS server, it must be able to resolve this URL and connect to it via that URL. Since this FS service is published via two different UAG servers, both sides of the users must be able access it via the same URL.

The easiest and most common way to satisfy this requirement is by having “split-brain” or dual zone DNS design. Basically, companies would have two different zones with the same name, one exposed to the Internet and one that is only internal. Figure 4 gives a visual demonstration of this requirement.

image

Figure 4: Split brain dual zone DNS design

Let’s review how different users would authenticate into the Gateway and access published applications. First, we will start with internally based users. Figure 5 provides a high level flow of how internal users will authenticate to the internal UAG server. For internal users whose domain was federated with Gateway, they will use the ADFS trunk as their primary portal. When they try to authenticate, they will be using Federated WebSSO, with first step (1a) accessing RP-STS and performing a home realm discovery, which will redirect them to their internal IDP-STS in step 1b, where they get their initial SAML token, which will be provided back to RP-STS (step 1c). RP-STS will issue the final token, which the client will provide to the ADFS trunk (step 1d), and the user is authenticated to the portal.

image

Figure 5: Internal user authentication to UAG

After successful authentication, the user will see a list of applications published to him via the AD FS trunk. The authorization to see these applications must be done via contents of the claims. Using normal security groups from Gateway AD will no longer work because the internal user actually does not use Gateway AD for authentication to the portal.

There are two types of applications that are supported via AD FS enabled trunks: Kerberos Applications and Claims-enabled applications.

In this solution, FIM 2010 R2 must be published to the internal users so they can get into the FIM 2010 R2 portal and perform administrative tasks, such as approve or deny external user account requests. FIM R2 is not a claims-enabled application, but it is a Kerberos based application and it can be published via AD FS enabled trunk by using Kerberos Constrained Delegation. Of course for this to work, the Gateway AD must have a shadow account for internal users. FIM R2 will actually help with creating shadow accounts. It is configured to synchronize internal Fabrikam AD user accounts into the Gateway AD, thus creating a shadow account for internal users. It will not synchronize user passwords into Gateway AD.

image

Figure 6: Internal user accessing Kerberos Applications

Internal users will be able to access FIM R2 via SSO experience and perform their work as needed. Figure 6 shows the basic authentication step for Kerberos based application. In the future, this solution will be able to publish other Kerberos based applications, and they will be accessed in the same way as FIM 2010 R2. They will require proper SPN configuration and Gateway AD, but users will already have shadow accounts.

The other type of applications that can be published via AD FS enabled trunks are claims-based applications. These are easy and straight forward to publish and access via AD FS trunk. Figure 7 provides a high level authentication flow for internal users.

The interesting part in this authentication flow and what is different from the original authentication to the portal itself is the fact that the client does not need to get another security token from its internal IdP-STS. Since he is already authenticated to the portal, after the client tries to access the published application, the client browser will only need to request a new security token from RP-STS, specific for this application, as it shown in Figure 7.

image

Figure 7: Internal user accessing claims applications

Finally, we can examine authentication flow and application access by external users. There will be two types of external users: users with accounts registered in the Gateway AD for which they know their passwords and federated users, whose identity belongs to some other organization. Each user type will have to use different trunks for authentication.

External users with accounts in Gateway AD will be accessing it by using a UAG trunk with Gateway AD as the primary authentication provider. The primary reason for this configuration is to allow these users to change their passwords and to notify them when their password is about to expire. Trunks that use AD FS as the primary authentication provider do not provide password management functions.

Federated external users will access the portal via UAG trunks with the AD FS server as the primary authentication provider. While these users are important to the future of this solution, the current primary user base will consist of external users with accounts in Gateway AD, and, for this reason, Figure 29 shows the authentication flow and access to applications for these types of users only.

First, the user will need to authenticate into the portal, which will be done via UAG forms based authentication with Gateway AD account. After successful authentication into the portal, the user will be presented with a list of applications, which he/she has been authorized to access. The authorization is based on the AD group membership. The authentication flow to the application will depend on the application type.

Non-claims enabled applications are actually very straightforward. For example, FIM 2010 R2 will be published to external users by using SSO function of the UAG trunks, and it will use the same authentication provider as for the trunk itself. Users will access such applications by utilizing their AD credentials, with UAG taking care of this authentication behind the scenes and without any special type of configuration requirements. This flow is shown as step 2 to Kerberos enabled applications.

Authentication to claims-enabled applications will be a bit more complex. Figure 8 shows it with step 3 flow. The application is published via the FBA trunk portal, and the user will try to access it via that portal. With step 3a, it will contact the application and learn that the application trusts RP-STS. RP-STS is not published via FBA trunk. It is published via ADFS Trunk, a different trunk on the UAG server. In step 3b, the user’s browser will be redirected to the RP-STS to get the token for the target application. Theoretically, we could issue a SAML token at this point in time, but since RP-STS is not published via an FBA Trunk, we will not be able to provide SSO experience to the end user. If we would end the process here, the user would be required to authenticate to RP-STS. Since there is no SSO for this user on the ADFS trunk, he/she will be prompted for credentials. Instead, the Home Realm Discovery will happen, and the user will be redirected to the IdP-STS (fs1.fabrikam.com). IdP-STS is published on the FBA trunk, and it is configured with SSO authentication via Gateway AD. The user is already authenticated to the FBA trunk and via step 3c will authenticate to the IdP-STS and receive security token. This token will be posted back to the RP-STS in step 3d, which will be transformed into a new token, suitable for the target application. It will be provided back to the client computer and posted to the application via FBA trunk in step 3e. The application will authenticate the user and open in the user’s browser.

image

Figure 8: External User Authentication and Application Access

It is not the most straightforward authentication experience, but as discussed earlier in this paper, configuration of claims-based applications with multiple UAG trunks requires separation between Resource Provider STS and Identity provider STS. Otherwise it will not be published via different UAG trunks.

Authentication of a federated user via an external UAG server is done the same way. It is for internal Fabrikam users, straight forward federated WebSSO.

Things to know about this design:

During the implementation of this solution, we discovered a few restrictions in AD FS that would not be very obvious if we used only one UAG server. However with dual implementation and especially with identical name spaces on Internet and Intranet, we ran into some minor constraints. Fortunately, fairly easy workaround were quickly identified to bypass them.

The first constraint is related to the certificate usage on AD FS. It will not allow the use of the same certificate (certificate with the same hash) on multiple relying parties. Why is this a problem? Since we have the identical name space on the internal network and external network, originally we tried to save on costs and use the same wild card certificate (*.fabrikam.com) on external UAG and internal UAG servers. UAG servers will work just fine with the same cert, but when time came to set them up as relying parties on the AD FS RP-STS server, we encountered a problem. AD FS did not allow the creation of the second relying party with a certificate whose hash had already been used by another relying party. The simple solution to get around this problem is to issue two different wild card certificates, one for internal UAG and one for external UAG. Usually these certificates must be trusted by Internet clients, so you would need to get them from one of the commercial certificate providers, and it will double your cost.

The second constraint is related to the naming of the ADFS Trunks on external and internal UAG servers and the potential conflict with RP-STS Federation Services for each relying party. During ADFS trunk configuration on the UAG server, it is most logical to configure the public URL for the trunk to match the URL of the published Federation server. By default, you would probably create the ADFS trunk for fs2.fabrikam.com AD FS with the same URL, i.e. it will be fs2.fabrikam.com. Then you would proceed to configure AD FS with the UAG relying party, which will configure it with the Federation Service URL as fs2.fabrikam.com. So far so good, we have no issues. Now, we proceed with the configuration of the second UAG server, where we create the UAG trunk for internal users, with the same URL, to match RP-STS, ie, fs2.fabrikam.com. This is done without any issues on the UAG server. The second step in configuration will be the creation of the relying party trust on the AD FS server. AD FS will not allow you to create the relying party trust to the second UAG server. This is because it is using the same URL as the first one, and AD FS will not allow two relaying parties with the same URL. Fortunately, there is a workaround for this as well. All you need to do is to configure each ADFS trunk with its own unique URL, different from the RP-STS URL. For example, the external UAG AD FS Trunk can be configured with the following URL for its public name: fs2e.fabrikam.com, and internal UAG AD FS trunk can be configured with the following URL for its public name: fs2i.fabrikam.com. When configuring each UAG server with RP-STS, they will appear as different relying parties, and AD FS will be happy. One thing to remember is to make sure that DNS is configured to resolve fs2.fabrikam.com to each respective UAG trunk, i.e. it needs to point to the same IP address as its internal or external public trunks URLs.

Thanks!

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October 18, 2011 · 10:42 pm

Designing UAG and AD FS Solution

In the last many posts we looked at all kind of different topologies for UAG and AD FS configuration.

Now, since we are armed with knowledge of different configuration options, we can put all of them to use and see how we can apply them to real life situations. Before we do this, we need to revisit some critical technical requirements that exist with UAG and ADFS v2.

  1. The UAG server can use the same AD FS v2 Federation Service URL only in one UAG trunk. This constraint is very important to understand because it is one of the critical elements that will affect your design.
  2. Based on the previous requirement, if your configuration requires multiple UAG trunks with AD FS v2 support, and we will examine shortly why this might be the case, you will need to implement a separate AD FS v2 server for each UAG trunk.
  3. UAG can provide Kerberos Constrained Delegation (KCD), but with the following constraints:
    • The UAG server must be in the same AD domain as the application server it is trying to access;
    • The User Account used to authenticate to the UAG server (the one we need to use KCD for) must be in the same AD Forest as the UAG server. If the user comes from a trusted AD Forest, the KCD will not work.

While designing your solution, you will have to gather a lot of requirements and understand the customer’s situation. Some requirements will force you into certain design topologies, and it is important to answer them at the beginning of the design process. There are at least three main questions that you have to answer when designing your UAG/ADFS access solution. The answers to these questions will direct you into a certain design topology or might require a combination.

The first question relates to password management. If you have a requirement to provide password management capabilities to remote users, -i.e. password change and notification of expiring password, you must use a UAG trunk that uses AD as the primary authentication provider. This type of trunk will authenticate you before providing access to any published applications. Access to claims based applications will be done via a secondary authentication to the back end published AD FS v2 server. This is the first topology that we discussed in the first part of this paper. Figure 1 shows this configuration.

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Figure 1: UAG with One Trunk and dedicated AD FS in each Trunk

The second question relates to strong authentication, i.e. Smart Card based authentication. If there is a requirement to provide Strong Authentication, then your remote access solution must have topology #2, with UAG trunk configured for Smart Card authentication against the Active Directory and the AD FS server configured as an authentication provider for the claims based application. Anytime there is a requirement to use Smart Card authentication on the UAG portal, it will consume at least one AD FS Federation Service. Since we cannot use the same trunk to provide authentication via AD UserID/Password and Strong Authentication, the configuration will have at least two UAG trunks. Figure 2 shows this configuration.

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Figure 2: UAG with Two Trunks and dedicated AD FS in each Trunk

The third question relates to the federation requirements with other companies. We need to identify if there is a federation requirement with external partners, specifically with IDP partners, where your company provides application resource for their use. If there is none, then our solution encompasses topology #1 and/or #2. If you must support federation as RP STS, then it complicates things. UAG trunks used for FBA or Smart Card authentication will consume their AD FS Federation Services, and it cannot be used by another trunk on the same UAG server.

We must implement yet another AD FS Federation Service on the internal network. If you need to satisfy all three requirements, you will need to have at least three UAG trunks, each with its own dedicated AD FS v2 server. Figure 3 shows this configuration.

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Figure 3: UAG with Three Trunks and dedicated AD FS in each Trunk

As you see in Figure 3, this is not a simple solution anymore. While we can use the same UAG server to publish all of these services and all kinds of applications, we must implement three separate AD FS services. However, this is not the end of the complications. There are still some critical design decisions that you must make. What is the ultimate goal of this solution? Yes, the goal is to publish applications to the end users. And what type of applications are we trying to publish via UAG/ADFS configuration? We are trying to publish claims based applications. Let’s think for a moment about configuration requirements for claims-based application. The first and foremost requirement is that it must be configured with a trusted Security Token Service. It must be able to accept security tokens from trusted STS for user authentication.

How would we need to configure the claims-based application with multiple AD FS v2 servers and multiple UAG trunks? The first logical way to look at it is by creating trusts between the target application and each STS. As shown in Figure 4, in such configuration each trunk will have its own AD FS server which will be able to issue security tokens to the application. The problem with this approach resides with Home Realm Discovery. If we configure the application to trust multiple STSs, we have to make some type of determination at the application level of where the user must authenticate to get the valid security token. We are taking Home Realm Discovery out of the AD FS realm and trying to do it at the application level. While theoretically it is possible, the reality is that applications are not designed to do Home Realm Discovery. The underlying Windows Identity Foundation service must be extended to provide this functionality, which is not very easy to do and, in most situations, is not the best practice. The goal behind claims based authentication is to simplify authentication and simplify the application developer’s life, thus outsourcing authentication related Home Realm Discovery functions to the services designed for this purpose. The bottom line is that setting the application with multiple STSs is not recommended, and it is not the best practice.

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Figure 4: Application with multiple RP-STS

The other common way to configure claims-based application is with one STS. Usually it will be designated as the Resource Provider role (RP-STS) and let RP-STS issue all security tokens for this application. RP-STS will be required to route user requests destined for other Identity providers. In our configuration, one of the AD FSv2 servers will be acting in this role. Which one should it be? The STS published via federated UAG trunk, (i.e. with UAG acting as AD FS proxy,) is the right choice for RP-STS. The configuration is shown in Figure 5.

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Figure 5: Application with dedicated RP-STS

This is a complex solution, but if you must have at least two UAG trunks with support for claims-based applications, this is the only viable choice to publish them.

In the next post we will take a look at a specific real world example of how UAG and AD FS can be used to publish applications.

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October 17, 2011 · 10:50 pm

UAG and ADFS Better Together–Authentication via Azure ACS

This post discussing how it is possible to publish applications to Internet based users who authenticate to the UAG via one of the Internet Cloud Identity Providers, such as LiveID, Google, Yahoo or Facebook. The Windows Azure ACS acts as IdP-STS in this configuration topology.

This is essentially the same as what we discussed in the previous configuration, where we published applications to partner organizations. The key difference here is that we do not actually have a specific individual organization. In this configuration, we are able to provide access to our applications to anyone who already has an identity at one of the big Cloud Identity providers – Microsoft LiveID, Google, Yahoo and Facebook. This accounts for millions of users.

The Microsoft Cloud development platform, Azure, provides this very unique capability via Azure Access Control Services. Azure ACS is configured to use these four identity providers as a potential authentication source. Very minimum configuration is required. Azure ACS must be configured as a trusted Identity provider with our internal RP-STS. From there on, the authentication is very similar to Federated WebSSO.

After the user tries to access the published application, he will be redirected to the RP-STS. Home Realm Discovery will be done at this point, and the user will be redirected to the Identity Provider, in this case Azure ACS. Depending on how Azure ACS is configured, it will redirect the user to one of the Cloud providers or it will give the user the option to choose one of them. The user will authenticate to the Cloud Identity provider and will be redirected back to Azure ACS, which, in turn, will create a SAML security token, provide it to the user, and from there on it will be posted back to RP-STS, transformed, and provided to the target application. Figure 1 shows the high level configuration for this topology.

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Figure 1: Azure ACS in Federated WebSSO

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October 2, 2011 · 10:59 am

UAG and ADFS Better Together–Publishing Applications to Partner Organizations

In this scenario, our partner organization users access claims based applications published by our organization UAG servers. The partner users provide security tokens issued by the partner controlled Identity Provider to our AD FS v2 published by the UAG server. This configuration is the most common federated access scenario, and UAG works very nicely to make it all happen.

The ultimate goal of such configuration is to provide a SSO experience to the end user and never ask them for additional credentials or any type of questions. There are two main areas that must be properly configured to accommodate SSO. The first one is part of the partner organization configuration. Their IdP must be able to authenticate the user on their internal network via SSO. This is easily done if IdP is using AD FSv2. As part of the same AD Forest, it will authenticate internal users via Windows Integrated Authentication and will issue the required security tokens. The second part in this configuration is to configure Home Realm discovery. RP-STS residing on our network (woodgrovebank.com) is probably acting as IdP for internal users, or it might have more Federated trusts with other IdPs. The proper configuration of Home realm discovery is important in Federated configurations so that users are not confused where they need to authenticate and that they might not need to see other partners in your organization. Home realm discovery can be configured via multiple ways and is a topic of its own. We will cover it sometime in future updates to this paper or via a separate article.

Figure 1 shows the overall topology for federated application publishing. If you are familiar with all previous topologies, then you can see how this will work, as it is pretty much an extension on all the previous configurations. Let’s take a look via Figure 2 at the high level authentication flow.

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Figure 1: Federated WebSSO Components

  1. First, the remote user will try to access the application published via the UAG server. Since the application is configured to work over claims-based authentication, it will redirect the browser to its RP-STS.
  2. RP-STS can be published on the same UAG trunk as our application. This trunk must not use internal AD for authentication. It must be configured as AD FS proxy trunk with RP-STS as the AD FS server behind it – i.e. it must be acting as a relying party. The user will contact RP-STS to get the security token for our target application. This is when Home Realm discovery takes place. If Home Realm Discovery is not configured to automatically redirect this user to his own IdP, then he/she will be prompted to choose his IdP from a list of configured trusted IdPs.
  3. During this step, the browser is redirected to his IdP, and it will try to request a security token for RP-STS. IdP-STS and RP-STS have a trust relationship, and, based on the conditions of this relationship, the IdP-STS will issue a security token to the user.
  4. This token will be posted back to the RP-STS, where it will be evaluated and based on the configured rules, and transformed into a new security token with a new set of claims suitable for consumption by the target application.
  5. The token generated by the RP-STS is redirected back to the user computer, and then, in steps 6 and 7, this token is posted back to the target application. The application will make its authentication and authorization decisions based on the claims presented in the token.

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Figure 2: Federated WebSSO Authentication Flow

This topology is an extension of the third topology we discussed in this paper, (Authentication to UAG Portal via Claims Based Authentication and accessing internal claims based application,) and all of the specific configuration related to the UAG and AD FS server are generally the same as in that configuration. The main differences are related to the more complicated Home Realm Discovery configuration and configuration of the partner IdP-STS.

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September 24, 2011 · 10:26 am

UAG and AD FS are Better Together – Publishing Non-Claims Based Applications

In article “UAG and AD FS are Better Together – UAG as AD FS Proxy”  we explored how user authenticates to UAG portal via claims based authentication and then accesses claims based application published via UAG portal. But what if published application does not support claims based authentication, after all how many applications out there that do? Fortunately, UAG is capable to publish and provide SSO experience for non-claims based applications as well. The caveat here is that they must support Kerberos authentication. If you remember this “UAG and ADFS are Better Together– Strong Authentication” topology where we provided access with strong authentication, we configured KCD authentication  between UAG and AD FS server. In this topology the configuration is slightly different but concept is the same. Instead of doing KCD between UAG and AD FS, we’ll need to configure KCD between UAG and the target application.

UAG is smart enough to transition from the claims based authentication and request Kerberos ticket from AD Domain Controller on behalf of the user. During application configuration you’ll need to specify what claim you’d like to use as a leading value to get the Kerberos ticket. UPN is a good choice. Also, the proper SPN must be configured in AD for the target application.

Figure 1 shows main aspects of this configuration and Figure 2 provides high level authentication steps of how this works. It is very similar to the previous configurations, just in slightly different order.

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Figure 1

  1. First, user must authenticate to the portal with SAML token, this is done via authentication to the backend AD FS server.
  2. When user tries to access published application that was configured with Kerberos Authentication, the UAG server will contact AD Domain Controller and will get Kerberos Service ticket for the target application. It will use the claim value that was configured with this application in its request to Domain Controller.
  3. Then UAG will send Kerberos ticket to the target application. Application will use the Kerberos ticket for authentication and authorization decision.
  4. If authentication was successful target application will allow access to the end user.

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Figure 2

This configuration has similar constraints as was discussed in topology with Smart Card authentication, they relate to the Kerberos constraints. In this configuration application servers must reside in the same Active Directory Domain as UAG server (obviously that means that UAG must belong to AD domain) and the user account must be in the same Active Directory Forest as UAG server as well. Also, there are requirements on the Domain and Forest Functional level, it must be at least at Windows 2003 level.

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