Post Syndicated from Ron Cully original https://aws.amazon.com/blogs/security/how-to-easily-log-on-to-aws-services-by-using-your-on-premises-active-directory/

AWS Directory Service for Microsoft Active Directory (Enterprise Edition), also known as Microsoft AD, now enables your users to log on with just their on-premises Active Directory (AD) user name—no domain name is required. This new domainless logon feature makes it easier to set up connections to your on-premises AD for use with applications such as Amazon WorkSpaces and Amazon QuickSight, and it keeps the user logon experience free from network naming. This new interforest trusts capability is now available when using Microsoft AD with Amazon WorkSpaces and Amazon QuickSight Enterprise Edition.

In this blog post, I explain how Microsoft AD domainless logon works with AD interforest trusts, and I show an example of setting up Amazon WorkSpaces to use this capability.

To follow along, you must have already implemented an on-premises AD infrastructure. You will also need to have an AWS account with an Amazon Virtual Private Cloud (Amazon VPC). I start with some basic concepts to explain domainless logon. If you have prior knowledge of AD domain names, NetBIOS names, logon names, and AD trusts, you can skip the following “Concepts” section and move ahead to the “Interforest Trust with Domainless Logon” section.

Concepts: AD domain names, NetBIOS names, logon names, and AD trusts

AD directories are distributed hierarchical databases that run on one or more domain controllers. AD directories comprise a forest that contains one or more domains. Each forest has a root domain and a global catalog that runs on at least one domain controller. Optionally, a forest may contain child domains as a way to organize and delegate administration of objects. The domains contain user accounts each with a logon name. Domains also contain objects such as groups, computers, and policies; however, these are outside the scope of this blog post. When child domains exist in a forest, root domains are frequently unused for user accounts. The global catalog contains a list of all user accounts for all domains within the forest, similar to a searchable phonebook listing of all domain accounts. The following diagram illustrates the basic structure and naming of a forest for the company example.com.

Domain names

AD domains are Domain Name Service (DNS) names, and domain names are used to locate user accounts and other objects in the directory. A forest has one root domain, and its name consists of a prefix name and a suffix name. Often administrators configure their forest suffix to be the registered DNS name for their organization (for example, example.com) and the prefix is a name associated with their forest root domain (for example, us). Child domain names consist of a prefix followed by the root domain name. For example, let’s say you have a root domain us.example.com, and you created a child domain for your sales organization with a prefix of sales. The FQDN is the domain prefix of the child domain combined with the root domain prefix and the organization suffix, all separated by periods (“.”). In this example, the FQDN for the sales domain is sales.us.example.com.

NetBIOS names

NetBIOS is a legacy application programming interface (API) that worked over network protocols. NetBIOS names were used to locate services in the network and, for compatibility with legacy applications, AD associates a NetBIOS name with each domain in the directory. Today, NetBIOS names continue to be used as simplified names to find user accounts and services that are managed within AD and must be unique within the forest and any trusted forests (see “Interforest trusts” section that follows). NetBIOS names must be 15 or fewer characters long.

For this post, I have chosen the following strategy to ensure that my NetBIOS names are unique across all domains and all forests. For my root domain, I concatenate the root domain prefix with the forest suffix, without the .com and without the periods. In this case, usexample is the NetBIOS name for my root domain us.example.com. For my child domains, I concatenate the child domain prefix with the root domain prefix without periods. This results in salesus as the NetBIOS name for the child domain sales.us.example.com. For my example, I can use the NetBIOS name salesus instead of the FQDN sales.us.example.com when searching for users in the sales domain.

Logon names

Logon names are used to log on to Active Directory and must be 20 or fewer characters long (for example, jsmith or dadams). Logon names must be unique within a domain, but they do not have to be unique between different domains in the same forest. For example, there can be only one dadams in the sales.us.example.com (salesus) domain, but there could also be a dadams in the hr.us.example.com (hrus) domain. When possible, it is a best practice for logon names to be unique across all forests and domains in your AD infrastructure. By doing so, you can typically use the AD logon name as a person’s email name (the local-part of an email address), and your forest suffix as the email domain (for example, [email protected]). This way, end users only have one name to remember for email and logging on to AD. Failure to use unique logon names results in some people having different logon and email names.

For example, let’s say there is a Daryl Adams in hrus with a logon name of dadams and a Dale Adams in salesus with a logon name of dadams. The company is using example.com as its email domain. Because email requires addresses to be unique, you can only have one [email protected] email address. Therefore, you would have to give one of these two people (let’s say Dale Adams) a different email address such as [email protected]. Now Dale has to remember to logon to the network as dadams (the AD logon name) but have an email name of daleadams. If unique user names were assigned instead, Dale could have a logon name of daleadams and an email name of daleadams.

Logging on to AD

To allow AD to find user accounts in the forest during log on, users must include their logon name and the FQDN or the NetBIOS name for the domain where their account is located. Frequently, the computers used by people are joined to the same domain as the user’s account. The Windows desktop logon screen chooses the computer’s domain as the default domain for logon, so users typically only need to type their logon name and password. However, if the computer is joined to a different domain than the user, the user’s FQDN or NetBIOS name are also required.

For example, suppose jsmith has an account in sales.us.example.com, and the domain has a NetBIOS name salesus. Suppose jsmith tries to log on using a shared computer that is in the computers.us.example.com domain with a NetBIOS name of uscomputers. The computer defaults the logon domain to uscomputers, but jsmith does not exist in the uscomputers domain. Therefore, jsmith must type her logon name and her FQDN or NetBIOS name in the user name field of the Windows logon screen. Windows supports multiple syntaxes to do this including NetBIOS\username (salesus\jsmith) and FQDN\username (sales.us.com\jsmith).

Interforest trusts

Most organizations have a single AD forest in which to manage user accounts, computers, printers, services, and other objects. Within a single forest, AD uses a transitive trust between all of its domains. A transitive trust means that within a trust, domains trust users, computers, and services that exist in other domains in the same forest. For example, a printer in printers.us.example.com trusts sales.us.example.com\jsmith. As long as jsmith is given permissions to do so, jsmith can use the printer in printers.us.example.com.

An organization at times might need two or more forests. When multiple forests are used, it is often desirable to allow a user in one forest to access a resource, such as a web application, in a different forest. However, trusts do not work between forests unless the administrators of the two forests agree to set up a trust.

For example, suppose a company that has a root domain of us.example.com has another forest in the EU with a root domain of eu.example.com. The company wants to let users from both forests share the same printers to accommodate employees who travel between locations. By creating an interforest trust between the two forests, this can be accomplished. In the following diagram, I illustrate that us.example.com trusts users from eu.example.com, and the forest eu.example.com trusts users from us.example.com through a two-way forest trust.

In rare cases, an organization may require three or more forests. Unlike domain trusts within a single forest, interforest trusts are not transitive. That means, for example, that if the forest us.example.com trusts eu.example.com, and eu.example.com trusts jp.example.com, us.example.com does not automatically trust jp.example.com. For us.example.com to trust jp.example.com, an explicit, separate trust must be created between these two forests.

When setting up trusts, there is a notion of trust direction. The direction of the trust determines which forest is trusting and which forest is trusted. In a one-way trust, one forest is the trusting forest, and the other is the trusted forest. The direction of the trust is from the trusting forest to the trusted forest. A two-way trust is simply two one-way trusts going in opposite directions; in this case, both forests are both trusting and trusted.

Microsoft Windows and AD use an authentication technology called Kerberos. After a user logs on to AD, Kerberos gives the user’s Windows account a Kerberos ticket that can be used to access services. Within a forest, the ticket can be presented to services such as web applications to prove who the user is, without the user providing a logon name and password again. Without a trust, the Kerberos ticket from one forest will not be honored in a different forest. In a trust, the trusting forest agrees to trust users who have logged on to the trusted forest, by trusting the Kerberos ticket from the trusted forest. With a trust, the user account associated with the Kerberos ticket can access services in the trusting forest if the user account has been granted permissions to use the resource in the trusting forest.

Interforest Trust with Domainless Logon

For many users, remembering domain names or NetBIOS names has been a source of numerous technical support calls. With the new updates to Microsoft AD, AWS applications such as Amazon WorkSpaces can be updated to support domainless logon through interforest trusts between Microsoft AD and your on-premises AD. Domainless logon eliminates the need for people to enter a domain name or a NetBIOS name to log on if their logon name is unique across all forests and all domains.

As described in the “Concepts” section earlier in this post, AD authentication requires a logon name to be presented with an FQDN or NetBIOS name. If AD does not receive an FQDN or NetBIOS name, it cannot find the user account in the forest. Windows can partially hide domain details from users if the Windows computer is joined to the same domain in which the user’s account is located. For example, if jsmith in salesus uses a computer that is joined to the sales.us.example.com domain, jsmith does not have to remember her domain name or NetBIOS name. Instead, Windows uses the domain of the computer as the default domain to try when jsmith enters only her logon name. However, if jsmith is using a shared computer that is joined to the computers.us.example.com domain, jsmith must log on by specifying her domain of sales.us.example.com or her NetBIOS name salesus.

With domainless logon, Microsoft AD takes advantage of global catalogs, and because most user names are unique across an entire organization, the need for an FQDN or NetBIOS name for most users to log on is eliminated.

Let’s look at how domainless logon works.

AWS applications that use Directory Service use a similar AWS logon page and identical logon process. Unlike a Windows computer joined to a domain, the AWS logon page is associated with a Directory Service directory, but it is not associated with any particular domain. When Microsoft AD is used, the User name field of the logon page accepts an FQDN\logon name, NetBIOS\logon name, or just a logon name. For example, the logon screen will accept sales.us.example.com\jsmith, salesus\jsmith, or jsmith.

In the following example, the company example.com has a forest in the US and EU, and one in AWS using Microsoft AD. To make NetBIOS names unique, I use my naming strategy described earlier in the section “NetBIOS names.” For the US root domain, the FQDN is us.example.com,and the NetBIOS name is usexample. For the EU, the FQDN is eu.example.com and the NetBIOS is euexample. For AWS, the FQDN is aws.example.com and the NetBIOS awsexample. Continuing with my naming strategy, my unique child domains have the NetBIOS names salesus, hrus, saleseu, hreu. Each of the forests has a global catalog that lists all users from all domains within the forest. The following graphic illustrates the forest configuration.

As shown in the preceding diagram, the global catalog for the US forest contains a jsmith in sales and dadams in hr. For the EU, there is a dadams in sales and a tpella in hr, and the AWS forest has a bharvey. The users shown in green type (jsmith, tpella, and bharvey) have unique names across all forests in the trust and qualify for domainless logon. The two dadams shown in red do not qualify for domainless logon because the user name is not unique across all trusted forests.

As shown in the following diagram, when a user types in only a logon name (such as jsmith or dadams) without an FQDN or NetBIOS name, domainless logon simultaneously searches for a matching logon name in the global catalogs of the Microsoft AD forest (aws.example.com) and all trusted forests (us.example.com and eu.example.com). For jsmith, the domainless logon finds a single user account that matches the logon name in sales.us.example.com and adds the domain to the logon name before authenticating. If no accounts match the logon name, authentication fails before attempting to authenticate. If dadams in the EU attempts to use only his logon name, domainless logon finds two dadams users, one in hr.us.example.com and one in sales.eu.example.com. This ambiguity prevents domainless logon. To log on, dadams must provide his FQDN or NetBIOS name (in other words, sales.eu.example.com\dadams or saleseu\dadams).

Upon successful logon, the logon page caches in a cookie the logon name and domain that were used. In subsequent logons, the end user does not have to type anything except their password. Also, because the domain is cached, the global catalogs do not need to be searched on subsequent logons. This minimizes global catalog searching, maximizes logon performance, and eliminates the need for users to remember domains (in most cases).

To maximize security associated with domainless logon, all authentication failures result in an identical failure notification that tells the user to check their domain name, user name, and password before trying again. This prevents hackers from using error codes or failure messages to glean information about logon names and domains in your AD directory.

If you follow best practices so that all user names are unique across all domains and all forests, domainless logon eliminates the requirement for your users to remember their FQDN or NetBIOS name to log on. This simplifies the logon experience for end users and can reduce your technical support resources that you use currently to help end users with logging on.

Solution overview

In this example of domainless logon, I show how Amazon WorkSpaces can use your existing on-premises AD user accounts through Microsoft AD. This example requires:

1. An AWS account with an Amazon VPC.
2. An AWS Microsoft AD directory in your Amazon VPC.
3. An existing AD deployment in your on-premises network.
4. A secured network connection from your on-premises network to your Amazon VPC.
5. A two-way AD trust between your Microsoft AD and your on-premises AD.

I configure Amazon WorkSpaces to use a Microsoft AD directory that exists in the same Amazon VPC. The Microsoft AD directory is configured to have a two-way trust to the on-premises AD. Amazon WorkSpaces uses Microsoft AD and the two-way trust to find users in your on-premises AD and create Amazon WorkSpaces instances. After the instances are created, I send end users an invitation to use their Amazon WorkSpaces. The invitation includes a link for them to complete their configuration and a link to download an Amazon WorkSpaces client to their directory. When the user logs in to their Amazon WorkSpaces account, the user specifies the login name and password for their on-premises AD user account. Through the two-way trust between Microsoft AD and the on-premises AD, the user is authenticated and gains access to their Amazon WorkSpaces desktop.

Getting started

Now that we have covered how the pieces fit together and you understand how FQDN, NetBIOS, and logon names are used, let’s walk through the steps to use Microsoft AD with domainless logon to your on-premises AD for Amazon WorkSpaces.

Step 1 – Set up your Microsoft AD in your Amazon VPC

If you already have a Microsoft AD directory running, skip to Step 2. If you do not have a Microsoft AD directory to use with Amazon WorkSpaces, you can create the directory in the Directory Service console and attach to it from the Amazon WorkSpaces console, or you can create the directory within the Amazon WorkSpaces console.

To create the directory from Amazon WorkSpaces (as shown in the following screenshot):

1. Sign in to the AWS Management Console.
2. Under All services, choose WorkSpaces from the Desktop & App Streaming section.
3. Choose Get Started Now.
4. Choose Launch next to Advanced Setup, and then choose Create Microsoft AD.

To create the directory from the Directory Service console:

1. Sign in to the AWS Management Console.
2. Under Security & Identity, choose Directory Service.
3. Choose Get Started Now.
4. Choose Create Microsoft AD.
   

In this example, I use example.com as my organization name. The Directory DNS is the FQDN for the root domain, and it is aws.example.com in this example. For my NetBIOS name, I follow the naming model I showed earlier and use awsexample. Note that the Organization Name shown in the following screenshot is required only when creating a directory from Amazon WorkSpaces; it is not required when you create a Microsoft AD directory from the AWS Directory Service workflow.

For more details about Microsoft AD creation, review the steps in AWS Directory Service for Microsoft Active Directory (Enterprise Edition). After entering the required parameters, it may take up to 40 minutes for the directory to become active so that you might want to exit the console and come back later.

Note: First-time directory users receive 750 free directory hours.

Step 2 – Create a trust relationship between your Microsoft AD and on-premises domains

To create a trust relationship between your Microsoft AD and on-premises domains:

1. From the AWS Management Console, open Directory Service.
2. Locate the Microsoft AD directory to use with Amazon WorkSpaces and choose its Directory ID link (as highlighted in the following screenshot).
   
3. Choose the Trust relationships tab for the directory and follow the steps in Create a Trust Relationship (Microsoft AD) to create the trust relationships between your Microsoft AD and your on-premises domains.

For details about creating the two-way trust to your on-premises AD forest, see Tutorial: Create a Trust Relationship Between Your Microsoft AD on AWS and Your On-Premises Domain.

Step 3 – Create Amazon Workspaces for on-premises users

For details about getting started with Amazon WorkSpaces, see Getting Started with Amazon WorkSpaces. The following are the setup steps.

1. From the AWS Management Console, choose
2. Choose Directories in the left pane.
3. Locate and select the Microsoft AD directory that you set up in Steps 1 and 2.
4. If the Registered status for the directory says No, open the Actions menu and choose Register.
   
5. Wait until the Registered status changes to Yes. The status change should take only a few seconds.
6. Choose the WorkSpaces in the left pane.
7. Choose Launch WorkSpaces.
8. Select the Microsoft AD directory that you set up in Steps 1 and 2 and choose Next Step.
   

9. In the Select Users from Directory section, type a partial or full logon name, email address, or user name for an on-premises user for whom you want to create an Amazon WorkSpace and choose Search. The returned list of users should be the users from your on-premises AD forest.
10. In the returned results, scroll through the list and select the users for whom to create an Amazon WorkSpace and choose Add Selected. You may repeat the search and select processes until up to 20 users appear in the Amazon WorkSpaces list at the bottom of the screen. When finished, choose Next Step.
    
11. Select a bundle to be used for the Amazon WorkSpaces you are creating and choose Next Step.
12. Choose the Running Mode, Encryption settings, and configure any Tags. Choose Next Step.
13. Review the configuration of the Amazon WorkSpaces and click Launch WorkSpaces. It may take up to 20 minutes for the Amazon WorkSpaces to be available.
    

Step 4 – Invite the users to log in to their Amazon Workspaces

1. From the AWS Management Console, choose WorkSpaces from the Desktop & App Streaming section.
2. Choose the WorkSpaces menu item in the left pane.
3. Select the Amazon WorkSpaces you created in Step 3. Then choose the Actions menu and choose Invite User. A login email is sent to the users.
4. Copy the text from the Invite screen, then paste the text into an email to the user.

Step 5 – Users log in to their Amazon WorkSpace

1. The users receive their Amazon WorkSpaces invitations in email and follow the instructions to launch the Amazon WorkSpaces login screen.
2. Each user enters their user name and password.
3. After a successful login, future Amazon WorkSpaces logins from the same computer will present what the user last typed on the login screen. The user only needs to provide their password to complete the login. If only a login name were provided by the user in the last successful login, the domain for the user account is silently added to the subsequent login attempt.

To learn more about Directory Service, see the AWS Directory Service home page. If you have questions about Directory Service products, please post them on the Directory Service forum. To learn more about Amazon WorkSpaces, visit the Amazon WorkSpaces home page. For questions related to Amazon WorkSpaces, please post them on the Amazon WorkSpaces forum.

– Ron