In this article, you'll learn about design principles and dependencies for a Conditional Access scenario that's based on Zero Trust.
We'll start out with some design principles.
Conditional Access as a Zero Trust policy engine
The Microsoft approach to Zero Trust includes Conditional Access as the main policy engine. Here's an overview of that approach:
Download an SVG file of this architecture.
Conditional Access is used as the policy engine for a Zero Trust architecture that covers both policy definition and policy enforcement. Based on various signals or conditions, Conditional Access can block or give limited access to resources, as shown here:
Here's a more detailed view of the elements of Conditional Access and what it covers:
This diagram shows Conditional Access and related elements that can help protect user access to resources, as opposed to non-interactive or non-human access. The following diagram describes both types of identities.
Conditional Access has mainly been focusing on protecting access from interactive humans to resources. As the number of non-human identities grow, access from these must be considered as well. Microsoft offers two features related to protecting access to and from workload identities.
- Protecting access to applications represented by a workload identity that is not selectable in the Azure AD Conditional Access portal. This option is supported by using security attributes. Assigning a security attribute to workload identities and selecting these in the Azure AD Conditional Access portal is part of AAD P1 license.
- Protecting access to resources initiated by workload identities (service principals). A new feature "Microsoft Entra Workload Identies" is offered in a separate license that supports this scenario. It includes lifecycle management of workload identities including protecting access to resources with Conditional Access.
Enterprise access model
Microsoft has previously provided guidance and principles for access to on-premises resources based on a tiering model:
- Tier 0: Domain controllers, public key infrastructure (PKI), Active Directory Federation Services (AD FS) servers and management solutions that manage these servers
- Tier 1: Servers that host applications
- Tier 2: Client devices
This model is still relevant for on-premises resources. For helping to protect access to resources in the cloud, Microsoft recommends an access control strategy that:
- Is comprehensive and consistent.
- Rigorously applies security principles throughout the technology stack.
- Is flexible enough to meet the needs of your organization.
Based on these principles, Microsoft created the following enterprise access model:
The enterprise access model replaces the legacy tier model, which focused on containing unauthorized escalation of privilege in an on-premises Windows Server Active Directory environment. In the new model, Tier 0 expands to become the control plane, Tier 1 consists of the management and data plane, and Tier 2 covers user and app access.
Microsoft recommends moving control and management into cloud services that use Conditional Access as the main control plane and policy engine, thus defining and enforcing access.
You can extend the Azure Active Directory Conditional Access policy engine to other policy enforcement points, including:
- Modern applications: Applications that use modern authentication protocols.
- Legacy applications: Via Azure Active Directory (Azure AD) Application Proxy.
- VPN and remote access solutions: Solutions like Microsoft Always On VPN, Cisco AnyConnect, Palo Alto Networks, F5, Fortinet, Citrix, and Zscaler.
- Documents, email, and other files: Via Microsoft Information Protection.
- SaaS applications.
- Applications running in other clouds, like AWS or Google Cloud (based on federation).
Principles of Zero Trust
The three main Zero Trust principles that Microsoft defines seem to be understood, especially by security departments. However, sometimes the importance of usability is overlooked during the design of Zero Trust solutions.
Usability should always be considered an implicit principle.
Principles of Conditional Access
Based on the preceding information, here's a summary of suggested principles. Microsoft recommends that you create an access model based on Conditional Access that's aligned with the three main Microsoft Zero Trust principles:
- Move the control plane to the cloud. Integrate apps with Azure AD and protect them by using Conditional Access.
- Consider all clients to be external.
Use least privileged access
- Evaluate access based on compliance and risk, including user risk, sign-in risk, and device risk.
- Use these access priorities:
- Access the resource directly, using Conditional Access for protection.
- Publish access to the resource by using Azure AD Application Proxy, using Conditional Access for protection.
- Use Conditional Access—based VPN to access the resource. Restrict access to the level of the app or DNS name.
- Segment network infrastructure.
- Minimize use of enterprise PKI.
- Migrate single sign-on (SSO) from AD FS to password hash synchronization (PHS).
- Minimize dependencies on DCs by using Kerberos KDC in Azure AD.
- Move the management plane to the cloud. Manage devices by using Microsoft Endpoint Manager.
Here are some more detailed principles and recommended practices for Conditional Access:
- Apply Zero Trust principles to Conditional Access.
- Use report-only mode before putting a policy into production.
- Test both positive and negative scenarios.
- Use change and revision control on Conditional Access policies.
- Automate the management of Conditional Access policies by using tools like Azure DevOps / GitHub or Azure Logic Apps.
- Use block mode for general access only if and where you need to.
- Ensure that all applications and your platform are protected. Conditional Access has no implicit "deny all."
- Protect privileged users in all Microsoft 365 role-based access control (RBAC) systems.
- Require password change and multi-factor authentication for high-risk users and sign-ins (enforced by sign-in frequency).
- Restrict access from high-risk devices. Use an Intune compliance policy with a compliance check in Conditional Access.
- Protect privileged systems, like access to the admininistrator portals for Office 365, Azure, AWS, and Google Cloud.
- Prevent persistent browser sessions for admins and on untrusted devices.
- Block legacy authentication.
- Restrict access from unknown or unsupported device platforms.
- Require compliant device for access to resources, when possible.
- Restrict strong credential registration.
- Consider using default session policy that allows sessions to continue if there's an outage, if the appropriate conditions were satisfied before the outage.
Design dependencies and related technologies
The following diagram shows dependencies and related technologies. Some of the technologies are prerequisites for Conditional Access. Others depend on Conditional Access. The design described in this document mainly focuses on Conditional Access and not on the related technologies.
Conditional Access guidance
For more information, see Conditional Access design based on Zero Trust and personas.
This article is maintained by Microsoft. It was originally written by the following contributors.
- Claus Jespersen | Principal Consultant ID&Sec
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