How to Implement Advanced Conditional Access Policies in Microsoft 365 for Real-World Security Scenr
TLDR: This article explores advanced conditional access strategies in Microsoft 365, focusing on securing business data on unmanaged devices, managing contractors’ access, protecting sensitive content with authentication contexts, handling high-risk users, and controlling sign-in frequency and session persistence to enhance security without compromising productivity.
Conditional Access in Microsoft 365 is a powerful tool for securing your organization’s data and resources. While basic policies like requiring Multi-Factor Authentication (MFA) and blocking legacy authentication provide a solid foundation, real-world scenarios often demand more nuanced and flexible approaches. This article delves into advanced conditional access strategies to address common challenges such as managing contractors, securing sensitive content, handling risky users, and controlling session durations.
In a recent discussion, Jason shared his experience rolling out conditional access policies. While MFA was successfully implemented and guest access improved, two issues emerged:
- Contractors lost access to Teams because they often use personal devices.
- A marketing employee accessed the finance SharePoint site remotely from an unsecured location.
These challenges highlight the need for refined conditional access policies that balance security with productivity.
Beyond the Basics: Addressing Real-World Challenges
1. Managing Contractors and Temporary Staff
Contractors often have Microsoft 365 licenses but do not use company-managed devices. This creates risks as their personal devices may lack encryption, compliance, or control, potentially exposing company data if compromised.
The Real-World Approach
While ideally contractors should use company devices, practical constraints mean many use their own. Instead of banning personal devices outright, conditional access can limit risks by:
- Allowing contractors to access Microsoft 365 only through web browsers.
- Blocking desktop and mobile app access to prevent data syncing to unmanaged devices.
Implementing Contractor Policies
- Create a security group for contractors (e.g., “Conditional Access Contractors”).
- Configure a conditional access policy targeting this group to block mobile and desktop app access but allow browser access.
- In the SharePoint admin center, set unmanaged device access to “Allow limited web-only access,” preventing downloads, printing, or syncing.
- Create complementary policies enforcing app restrictions for SharePoint and OneDrive.
This approach enables contractors to collaborate securely without local data copies, balancing security and productivity.
2. Handling High-Risk Users
Microsoft Entra uses machine learning to detect compromised accounts based on signals like dark web credential leaks or unusual activity. When a user is marked as high risk, conditional access can automatically block access until remediation.
Setting Up High-Risk User Policies
- Create a conditional access policy targeting all users except break-glass accounts.
- Configure the policy to block access for users flagged with high user risk.
- Complement this with policies addressing high sign-in risk events.
This acts as a digital kill switch, instantly locking down compromised accounts.
3. Protecting Sensitive Content with Authentication Contexts
Sometimes blanket policies are too restrictive. Authentication contexts allow applying extra security controls to specific sensitive resources, such as finance or HR SharePoint sites.
How Authentication Contexts Work
- Define an authentication context (e.g., “Require compliant device for sensitive data”).
- Create a conditional access policy requiring compliant devices and phishing-resistant MFA for users accessing resources with this context.
- Apply the authentication context to specific SharePoint sites.
Applying Authentication Contexts to SharePoint Sites
Currently, applying authentication contexts to SharePoint sites is done via PowerShell:
- Connect to the SharePoint site.
- Assign the authentication context to the site.
- Verify the assignment.
Once applied, users must meet the enhanced security requirements to access the sensitive site.
4. Controlling Sign-In Frequency and Persistent Browser Sessions
Managing how long users stay signed in and whether sessions persist after closing the browser helps reduce risk from stolen session tokens.
Key Settings
- Sign-in Frequency: Determines how often users must reauthenticate (e.g., every 8 hours).
- Persistent Browser Session: Controls whether users stay signed in after closing the browser (e.g., set to “Never persistent” to require login each time).
Implementing Session Controls
- Create a conditional access policy targeting all users (excluding break-glass accounts).
- Set sign-in frequency to 8 hours.
- Set persistent browser session to never persistent.
This setup balances security with user convenience, ensuring sessions refresh regularly and users sign in anew after closing browsers.
Conclusion
Advanced conditional access policies in Microsoft 365 enable organizations to secure their environments effectively while accommodating real-world complexities. By:
- Restricting contractors to browser-only access,
- Automatically blocking high-risk users,
- Applying authentication contexts to sensitive content,
- Managing sign-in frequency and session persistence,
businesses can enhance security without hindering productivity.
Implementing these strategies requires careful planning and testing but results in a robust security posture tailored to organizational needs.
Embracing these advanced conditional access techniques will help protect your data and empower your workforce to work securely from anywhere.