Active Directory Certificate Services has long served certificate needs, but modern IT demands highlight its limitations in cloud environments, automation, scalability, and post-quantum readiness. Explore its merits, mitigations, and 10 key considerations for alternatives.

What Active Directory Certificate Services does

Evaluating the merits and limitations of relying on Active Directory Certificate Services (AD CS) for all certificate management needs in modern IT highlights that AD CS was fundamentally designed for on-premises deployment. Since its introduction in Windows 2000, it has successfully served private and public organisations as a critical solution for certificate issuance. However, the demands of modern IT present practical reasons to explore alternatives that are better suited to the contemporary landscape, which is increasingly decentralised, cloud-based, API-focused, and broadly adopting containerisation and related workloads.

Active Directory Certificate Services functions as a Microsoft Certificate Authority, issuing certificates and managing certificate templates within the Active Directory environment. The certificate templates folder and certificate template settings enable administrators to control how certificates are issued, whilst Active Directory integration provides automated certificate enrollment for domain-joined devices and users.

Why ADCS replacement matters

Modern organisations face challenges that AD CS struggles to address effectively. These limitations create security risks, operational inefficiencies, and barriers to digital transformation:

Modern deployment and cloud environments
AD CS struggles with containerisation, automation, and cloud-native applications due to its stateful nature and tight integration with Active Directory. Hybrid deployments that span both on-premises and cloud environments are inherently complex and require additional tools and configurations. As workloads move to the cloud, the relevance of AD CS diminishes due to its deep integration with Active Directory. Its stateful nature and tight integration with AD for authentication, authorization, and certificate management make it challenging to decouple from AD.

Security and multi-tenancy
Ensuring AD CS maintains its security posture in containerised environments requires careful planning. Its single-tenant architecture makes it unwieldy and costly at scale, leading to CA proliferation and complex management. Misconfigurations by administrators can introduce vulnerabilities, including excessive permissions, certificate template settings errors, and inadequate access controls that security teams must continuously monitor.

Post-quantum compatibility
Current versions of AD CS lack support for post-quantum cryptography (but it is coming). As quantum computing advances, traditional cryptographic algorithms like RSA and ECC are becoming vulnerable to quantum attacks. Microsoft AD CS has not yet integrated PQC algorithms, posing a significant risk for future-proofing security and data protection.

Operational and evolutionary challenges
Managing AD CS is resource-intensive, and it hasn't significantly evolved since 2012. It lacks support for IoT devices and connected vehicles. Misconfigurations introduce vulnerabilities that can disrupt business operations and create security risks across the Public Key Infrastructure PKI environment.

High availability and scalability
AD CS does not support active-active clustering and struggles to scale for millions of certificates issued. Its lack of multi-cloud and multi-OS support limits adaptability across different environments. Managing database files and ensuring high availability requires additional infrastructure and planning.

Certificate management limitations
The built-in AD CS tools are limited, lacking sufficient capabilities for tracking and reporting expired certificates. They do not support automation, such as integrating the deployment and installation of certificates to applications and hosts. Without centralized management capabilities, organizations struggle to maintain full visibility across their certificate estate, leading to certificate expiration incidents and service disruptions.

API and automation limitations
AD CS lacks comprehensive API support and integration with widely supported protocols like ACME, EST, and REST, limiting automation opportunities. This makes integration with DevOps tools and modern workflows difficult, creating manual processes prone to human error.

Dependency on RPC
AD CS's reliance on RPC/DCOM for certificate requests necessitates multiple ports, complicating firewall management and cloud integration. This architectural point creates challenges when organizations need to secure network access and control access across distributed environments.

Newer use cases
AD CS does not support emerging use cases like SSH certificates and Vehicle-to-Everything (V2X). As organizations adopt IoT devices and modern authentication methods, the limitations of Microsoft ADCS become more apparent.

Mitigations and merits of Active Directory Certificate Services

Let's review if mitigations exist for that comprehensive list.

Hybrid deployment support
Microsoft has enhanced AD CS's hybrid capabilities to address its limitations. A hybrid deployment integrates on-premises AD CS with cloud-based services like Microsoft Entra, leveraging both environments. Certificates for cloud services are issued by a combination of on-premises AD CS and cloud-based services. The "Hybrid Certificate Trust" model ensures certificates issued by AD CS are trusted across both environments, enabling seamless authentication and secure communication. Azure Key Vault provides Certificate Authority services, creating and managing certificates issued by public CAs or self-signed certificates. Microsoft Cloud PKI and Microsoft Azure services provide additional options for organizations within the Microsoft ecosystem.

Security enhancements
Microsoft is continually improving AD CS security features. Windows Server 2025 updates include new Kerberos features to minimize NTLM use, enhancing AD environments' overall security. Security teams benefit from improved monitoring capabilities and reduced attack surface when properly configured.

Modernization
Although AD CS isn't natively designed for containerisation or microservices, Microsoft provides guidance and tools for modernization. This includes leveraging Azure for hybrid deployments and using automation tools to streamline AD CS management. Organizations can install modern alternatives alongside existing AD CS infrastructure to support digital transformation whilst maintaining backwards compatibility with Windows servers and the Microsoft ecosystem.

Post-quantum readiness
Microsoft is preparing for quantum computing by integrating PQC algorithms into AD CS. Updates to SymCrypt and CNG support PQC algorithms, enabling AD CS to issue certificates with quantum-resistant cryptography. Transitioning to TLS 1.3 is emphasized for using quantum-safe key exchange and authentication methods.

Active Directory auto enrollment
On the merit side, although the deep integration with Active Directory can limit support for newer technologies like containerisation, it also enables automated certificate enrollment for Active Directory-enabled objects, such as workstations and servers, by leveraging Active Directory group policy. This auto enrollment capability reduces manual effort for provisioning certificates to domain-joined devices.

Web enrollment services
Similarly, although AD CS does not natively support REST APIs, third-party solutions and projects provide REST API interfaces for AD CS, enabling systems outside an Active Directory domain to request certificates via REST API calls. Additionally, the Certification Authority Web Enrollment service offers web pages that enable users to perform certificate tasks, such as requesting and renewing certificates.

Exploring modern alternatives: 10 important considerations

If these mitigations and merits aren't deemed sufficient due to the fundamental lack of support for modern deployment methods like containerisation and integration with orchestration and automation technologies, here are 10 important considerations to be kept in mind:

Certificate lifecycle management
Seek features such as automated discovery, renewal, and deployment of certificates to reduce manual effort and minimize human error. Ensure integration with popular orchestration tools, which will be facilitated by broad API support. The CLM should have the capability to integrate seamlessly with any existing AD CS infrastructure, providing complete visibility into certificate expiration and expired certificates across the environment.

2. Comprehensive visibility
Ensure the solution provides robust discovery tools to locate all certificates across various platforms, including servers, load balancers, firewalls, containers, and multi-cloud environments. Full visibility prevents certificate expiration incidents and enables security teams to maintain control over the entire certificate estate.

3. SaaS-based certificate management solution
Assess whether vendors offer a fully-featured SaaS solution that meets your organization's security requirements and use cases, helping to offload operational burden whilst providing scalability and flexibility.

Note of caution: While Cloud PKIs can simplify processes, they may also hide underlying complexities and depend on custom scripts. Additionally, keep the following in mind:

• Migration challenges: Difficulties in moving from one provider to another
• Business continuity: Risks if the provider ceases operations
• Provider decisions: Potential conflicts with your requirements

4. Post-quantum cryptography support
Provides support for post-quantum cryptography to future-proof your Public Key Infrastructure PKI against quantum computing threats.

5. Hardware Security Modules (HSM) support
Seamless integration with common industry Hardware Security Modules (HSM) solutions to protect private keys and CA certificates with robust data protection.

6. Integration with existing infrastructure
The solution should integrate with your existing systems, including Active Directory, cloud services, and orchestration tools like Kubernetes. Consider solutions that support AWS Private CA, Microsoft Azure, and other cloud environments whilst maintaining compatibility with on-premises Windows servers.

7. Scalability
Choose a solution that can scale with your organization's growth, managing an increasing number of certificates and supporting multi-cloud and multi-OS environments. Assess whether the solution supports multi-tenant configurations and the distribution of core Public Key Infrastructure components, such as Registration Authorities (RA) and Certification Authorities (CA), to provide robust security and flexible deployment options in complex and segmented network environments. Can the new CA handle issuing certificates at the required rate?

8. Security and compliance
The solution should provide comprehensive security features, including policy governance, compliance monitoring, and the capability to manage root of trust certificates. Ensure alignment with regulatory standards and the ability to control access and address security risks across different environments.

9. User interface and experience
A user-friendly interface and intuitive user experience are essential for efficient certificate management and ease of use. Security teams and administrators require centralized management capabilities that make sense for their operational workflows.

10. Assurance and governance
Audited against stringent standards such as PCI DSS and holding recognized certifications like Common Criteria. These assurances provide confidence that the solution meets enterprise requirements and regulatory standards.

Conclusions: supplement or replace Active Directory Certificate Services

While your AD CS implementation may have effectively met past requirements, it's essential to assess whether it aligns with current needs. If there's a significant gap between what is delivered and what is required, consider the following options:

Supplementation
Enhance AD CS by integrating it with CLM technology to incorporate features like automation, full visibility, and compliance. This approach makes sense for organizations heavily invested in the Microsoft ecosystem who need to address specific limitations whilst maintaining their existing Certificate Authority infrastructure.

Replacement
Take a more holistic approach and replace AD CS to better meet your current requirements by transitioning to a SaaS platform that supports a cloud-first strategy. Note that SaaS solutions include functionality that enables connectivity to AD CS servers, which can either be placed into continued service or serve as a migration stage before implementing newer SaaS Private CAs. Modern alternatives support provisioning certificates across cloud environments, integrate with DevOps tools, provide automation that reduces risk, and offer the flexibility needed for digital transformation without the limitations inherent in Microsoft ADCS.