Active Directory Certificate Services (AD CS) is Microsoft’s built-in Public Key Infrastructure (PKI) platform for issuing and managing X.509 certificates in Windows-centric environments. When it’s deployed well, it becomes the foundation for secure communications and identity-backed authentication across servers, users, devices, and applications: TLS for internal web apps, LDAPS, 802.1X (EAP-TLS), VPN authentication, device certificates for management tooling, smart card logon, and more.
At the same time, AD CS is easy to deploy in a way that “works” but is fragile: mis-scoped templates that issue overly powerful certificates, revocation endpoints that aren’t reachable when clients need them, CAs hosted on general-purpose servers without hardening, or designs that can’t scale beyond the first few use cases. This guide is written to help you deploy AD CS as an enterprise-grade PKI—starting with design decisions that determine long-term safety and maintainability, and then moving into installation, templates, autoenrollment, and revocation publishing.
The narrative assumes you’re an IT administrator or system engineer who needs practical guidance and correct defaults, not theoretical PKI material. Where options exist, you’ll see why they matter, what they cost operationally, and what tends to break in production if you skip them.
Define what you’re securing and why PKI is the right tool
A certificate binds an identity (a subject name and/or SAN—Subject Alternative Name) to a public key, and that binding is vouched for by a Certificate Authority (CA). Clients that trust the CA can validate certificates and establish secure channels (typically TLS) or use certificates for authentication (such as client TLS authentication, EAP-TLS, or smart card logon).
Before building anything, document the initial use cases you intend to support in the first 90 days. This is not bureaucracy; it directly drives template design, validity periods, key sizes, revocation lifetimes, and whether you need components like Online Responder (OCSP) or NDES for SCEP.
Common first-phase use cases in Windows environments include:
Server authentication certificates for IIS, SQL Server, Exchange, or internal APIs. These primarily need “Server Authentication” EKU and SANs.
LDAPS certificates for domain controllers. These require SANs that match how clients reach DCs (DNS names) and should be tightly automated.
Client authentication certificates for Wi-Fi/VPN via EAP-TLS, often issued to computers (for machine auth) and/or users.
Code signing or document signing (more specialized; typically you keep this isolated due to the impact of key compromise).
A real-world scenario that frequently drives an AD CS deployment is internal application modernization: a team migrates an internal API gateway to require mTLS (mutual TLS), but manual certificate issuance doesn’t scale and self-signed certificates break trust distribution. AD CS gives you centralized issuance, lifecycle management, and a trust anchor distributed via Active Directory.
The second scenario is security hardening driven by audit: a compliance review flags plaintext LDAP binds, and the organization commits to LDAPS. AD CS enables consistent DC certificates plus automated renewal, reducing the chance of service-impacting expirations.
A third scenario is wireless modernization: moving from PEAP-MSCHAPv2 to EAP-TLS for phishing-resistant Wi-Fi auth. That requires reliable user/computer certificate provisioning and a revocation model that won’t strand devices when they roam.
Those examples matter because AD CS design is not “one size fits all.” A PKI meant mainly for server TLS looks different from one that issues user authentication certificates at large scale.
Choose an enterprise PKI design: offline root and issuing CAs
AD CS supports multiple CA types. The core design decision is whether your root CA (the ultimate trust anchor) is online and domain-joined, or offline and isolated. For most enterprise deployments, the recommended pattern is:
An offline root CA (Standalone Root CA) that is not domain-joined and is powered on only for infrequent tasks like signing subordinate CA certificates and publishing updated CRLs.
One or more online issuing CAs (Enterprise Subordinate CAs) that are domain-joined and handle day-to-day certificate issuance using certificate templates and autoenrollment.
This structure limits blast radius. If an online issuing CA is compromised, you can revoke it at the root and replace it without changing the root trust anchor everywhere. If you instead run a single online Enterprise Root CA, compromise of that CA is catastrophic: you must re-establish trust for the entire environment.
An enterprise CA integrates with Active Directory. It publishes CA objects, uses certificate templates, and supports autoenrollment. A standalone CA does not use templates or autoenrollment and is typically used for the offline root role.
Capacity planning is straightforward for most environments: a single issuing CA can handle substantial issuance volume, but you should consider at least two issuing CAs for availability and administrative separation if PKI becomes mission critical (for example, if EAP-TLS is the primary Wi-Fi auth method).
You should also decide early whether to separate roles by function. Some organizations run one issuing CA for “general” TLS and one for “high assurance” templates (smart card logon, code signing). Separation can reduce risk by applying stricter issuance controls and more limited administrator access where it matters.
Establish naming, validity periods, and cryptographic baselines
Once you know the high-level CA hierarchy, define the naming conventions and cryptographic baselines. This avoids later pain where certificates don’t match expectations, renewal windows are inconsistent, or algorithms become a compliance issue.
For CA names, use stable, descriptive common names that won’t need changing if you reorganize server naming. A typical pattern is “Contoso Root CA” and “Contoso Issuing CA 01.” CA names become embedded in certificates and are painful to change.
For key algorithms, RSA remains widely compatible in Windows ecosystems, though ECDSA may be attractive for performance and smaller keys. The practical guidance for many mixed environments is RSA 2048 or RSA 3072 for issuing CAs and RSA 4096 for offline root CAs. If you have strict regulatory requirements, align with your policy; otherwise prefer compatibility.
Validity periods should reflect risk and operational reality. Typical baselines are:
Offline root CA certificate: 10–20 years.
Issuing CA certificate: 5–10 years.
End-entity certificates (server/client): 1 year or less. Shorter lifetimes reduce impact of private key compromise and reduce dependency on revocation, but increase renewal volume. With autoenrollment, one-year certificates are usually manageable.
Revocation infrastructure must support those choices. If you set short end-entity lifetimes, you can often keep CRL validity reasonable without huge risk; if certificates are long-lived, revocation becomes more critical.
A practical design checkpoint: if your organization has remote/off-network devices (laptops, VPN clients, mobile devices), ensure they can reach revocation endpoints and (if needed) AIA locations. An otherwise correct PKI design can fail simply because clients cannot fetch CRLs when offsite.
Plan CA placement, hardening, and administrative model
Your CA is a security boundary. Treat CA servers as tier-0 infrastructure, with administrative access controlled accordingly.
At minimum, plan for:
Dedicated servers (virtual or physical) for issuing CAs. Avoid co-hosting with application workloads.
Restricted administrator groups. Limit local admin and CA admin memberships. Use separate admin accounts and privileged access workstations where feasible.
Patch and backup strategy. A CA is not easily rebuilt without planning; its private key and database must be protected and recoverable.
If you can use an HSM (Hardware Security Module), it can protect CA private keys from extraction. That said, HSM integration adds cost and operational complexity. Many organizations start with software key storage (protected by strong OS controls) and add HSMs later for the most sensitive CAs.
Networking matters too. Issuing CAs should be reachable by domain members for enrollment, and they need outbound access to publish CRLs/AIA if those locations are HTTP-based on separate servers. Offline roots should be isolated and only connected when needed.
Role separation is where many deployments stumble. In AD CS, there are multiple administrative roles: CA administrators who manage the CA configuration, certificate managers who approve and manage requests, and template administrators (in AD) who manage templates. Keep those roles distinct where possible. A common safe approach is to centralize template changes with a small group and treat them like code changes: reviewed, tested, documented.
Design revocation and CA distribution points (CRL and AIA)
Two URLs embedded in certificates determine how clients validate chains and revocation status:
AIA (Authority Information Access): where clients can fetch issuing CA certificates.
CDP (CRL Distribution Point): where clients can fetch CRLs (Certificate Revocation Lists).
If those endpoints are wrong or unreachable, certificate validation can fail in ways that look random: an internal web app works on one subnet but fails for VPN users, or domain-joined servers validate quickly while non-domain clients hang during revocation checks.
A robust baseline is to publish CRL and AIA over HTTP from a highly available location (for example, an internal web server or a pair behind a load balancer). LDAP publishing to Active Directory also occurs automatically for enterprise CAs and helps domain-joined clients, but HTTP is still important for non-domain and off-network systems.
When you configure CDP/AIA, think about longevity. These URLs are embedded into issued certificates; changing them later doesn’t fix already-issued certificates. Use stable DNS names rather than server hostnames. Many organizations use something like:
Where pki.contoso.com resolves to a highly available web service.
CRL lifetimes are a trade-off. A common pattern is:
Base CRL: published daily or weekly with a validity of several days.
Delta CRL (optional): published more frequently for faster revocation propagation.
Not every environment needs delta CRLs, but if you intend to rely on revocation for user authentication (EAP-TLS, smart card logon), tighter revocation propagation can matter.
OCSP (Online Certificate Status Protocol) via the Online Responder role can reduce reliance on downloading CRLs and can speed up validation. It’s optional, but beneficial when you have many clients validating frequently (for example, high-traffic TLS termination or Wi-Fi auth).
Prepare Active Directory and DNS prerequisites
Because issuing CAs will be Enterprise CAs, ensure your Active Directory is healthy. AD CS relies on AD replication for template distribution and CA objects, and autoenrollment relies on Group Policy.
At a minimum:
Confirm time synchronization is solid. Kerberos and certificate validation are time-sensitive.
Ensure DNS is consistent and that you can reserve stable names for CDP/AIA endpoints (for example, pki.contoso.com).
Confirm AD functional level and Windows Server versions you’ll deploy. AD CS is available across multiple Windows Server versions, but you should standardize for supportability.
Also plan service accounts. Most AD CS roles run under local system by default; avoid unnecessary domain service accounts unless required by a specific integration.
If you plan to publish CRLs to an HTTP location, prepare that web server (IIS or other). It doesn’t need to be complex: a static file server with appropriate ACLs and availability. The important part is that CA servers can write CRL/AIA files to it (often via SMB to a share, then served by HTTP), while clients can read them over HTTP.
Build the offline root CA
The offline root CA is the trust anchor. Build it deliberately.
Start with a clean Windows Server installation (Server Core is often preferred to reduce attack surface, but full GUI is acceptable if your operations require it). Do not join it to the domain. Apply security baselines, disable unnecessary services, and configure strong local administrator credentials stored securely.
Install the AD CS Certification Authority role as a Standalone Root CA. You can install via Server Manager or PowerShell. PowerShell is repeatable and easier to document.
Install-WindowsFeature ADCS-Cert-Authority -IncludeManagementTools
Install-AdcsCertificationAuthority \
-CAType StandaloneRootCA \
-CACommonName "Contoso Root CA" \
-KeyLength 4096 \
-HashAlgorithmName SHA256 \
-ValidityPeriod Years \
-ValidityPeriodUnits 15
After installation, configure CDP and AIA locations. For an offline root, you usually publish the root CA certificate and CRL to a location that clients can reach, but you do not want the root to depend on network availability. The operational model is:
Generate root CRL and root CA certificate.
Copy them via removable media to the web/HTTP publication point.
Publish them on the HTTP server so all clients can retrieve them.
Also publish the root CA certificate into Active Directory so domain members trust it automatically. Because the root is offline and standalone, you typically export and import the root certificate into AD using a domain-joined admin workstation.
On the root CA, export the root CA certificate:
powershell
certutil -ca.cert ContosoRootCA.cer
Publish to Active Directory (run on a domain-joined machine with appropriate privileges):
powershell
certutil -dspublish -f ContosoRootCA.cer RootCA
certutil -dspublish -f ContosoRootCA.cer NTAuthCA
The NTAuth store publication is important if you will use the PKI for smart card logon or other scenarios that require the issuing chain to be trusted for authentication. Even if you don’t need it on day one, planning for it now avoids later confusion.
Next, generate and publish the root CRL:
powershell
certutil -crl
Copy the generated .crl file and the root .cer file to your HTTP publication directory (for example, on the server behind pki.contoso.com). Ensure they are accessible via the exact URLs you plan to embed.
Because the root is offline, set CRL validity long enough to avoid frequent root power-ons, but not so long that revocation becomes meaningless. Many organizations publish a root CRL valid for 6–12 months and refresh it on a scheduled cadence.
Install the enterprise issuing CA (online subordinate)
With the root CA established and its certificate published, you can deploy the issuing CA. This is the CA your servers and users will talk to for enrollment and renewal.
Provision a dedicated Windows Server, join it to the domain, and ensure it is patched. Decide whether to use Server Core or full UI. For many organizations, Server Core reduces attack surface and is perfectly manageable via remote tools.
Install the AD CS CA role and configure it as an Enterprise Subordinate CA. You will generate a certificate request for the subordinate CA, have the offline root sign it, then install the resulting CA certificate.
powershell
Install-WindowsFeature ADCS-Cert-Authority -IncludeManagementTools
Install-AdcsCertificationAuthority \
-CAType EnterpriseSubordinateCA \
-CACommonName "Contoso Issuing CA 01" \
-KeyLength 3072 \
-HashAlgorithmName SHA256 \
-ValidityPeriod Years \
-ValidityPeriodUnits 8
During setup, the wizard/command will generate a subordinate CA request (a .req file). Copy that request to the offline root CA via secure means.
On the offline root CA, sign the subordinate request:
powershell
certreq -submit ContosoIssuingCA01.req
If you’re using the CA UI you will select the request and issue it. Export the issued subordinate CA certificate (and ideally the chain) and copy it back to the issuing CA.
On the issuing CA, complete the installation by installing the CA certificate:
powershell
certutil -installcert ContosoIssuingCA01.cer
Once the issuing CA is online, confirm it can publish to Active Directory and that domain members can build a chain to the root. At this stage, you have the skeleton of an enterprise PKI, but it won’t be usable at scale until templates and autoenrollment are configured.
Configure CDP/AIA on the issuing CA and publish CRLs
The issuing CA’s CDP/AIA configuration is one of the most consequential settings because it affects every certificate you issue.
In the Certification Authority console (certsrv.msc), open CA properties and review the Extensions tab. Ensure you have:
HTTP CDP location that points to your stable PKI URL (pki.contoso.com).
HTTP AIA location for the issuing CA certificate.
LDAP locations are typically present for enterprise CAs; keep them unless you have a reason not to.
After you add or correct CDP/AIA locations, you must publish a new CRL and (depending on changes) restart the CA service. More importantly, recognize that changes only affect certificates issued after the change.
A common operational model is:
CA writes CRL/AIA to a local folder.
A scheduled job copies files to an SMB share on the web server.
IIS serves those files over HTTP.
That model avoids granting the CA direct write access to a web root and provides clean separation.
Ensure file permissions are correct: the CA needs to write, the web server needs to read, and clients need HTTP read access.
Publish a base CRL:
powershell
certutil -crl
Then verify reachability from multiple network segments:
powershell
# From a client
certutil -url http://pki.contoso.com/pki/Contoso%20Issuing%20CA%2001.crl
If you plan to support remote clients over VPN or the internet, validate access from those paths as well. A very common failure mode is that revocation URLs are only reachable internally, which can cause TLS handshakes to hang or fail for remote users.
Create and govern certificate templates
Certificate templates are the mechanism that makes AD CS manageable. A template defines what a certificate can be used for (Enhanced Key Usage/EKU), how the subject name is built, key properties, enrollment permissions, and renewal behavior.
Start from least privilege: create templates that issue exactly what a use case needs, to the smallest set of identities possible. Avoid using overly permissive templates like “User” or “Computer” as-is for authentication scenarios without reviewing EKUs, subject name settings, and permissions.
You manage templates in the Certificate Templates console (certtmpl.msc). The typical workflow is:
Duplicate an existing Microsoft template close to your desired use.
Adjust cryptographic settings and subject name settings.
Set security permissions for enrollment and autoenrollment.
Publish the template on the issuing CA.
A key security concept: if a template allows the requester to supply the subject name (or SAN) and grants enrollment to a broad group, it can enable impersonation. For example, a user could request a certificate for a privileged server name and use it for TLS or client auth in unintended ways. For most enterprise templates, you want the CA to build the subject from Active Directory information rather than accepting arbitrary input.
Also understand manager approval and authorized signatures. For high-risk certificates (code signing, smart card logon in some models), you may require approval, but that increases operational overhead. Many organizations reserve approval workflows for only the most sensitive templates.
Implement autoenrollment with Group Policy
Autoenrollment is what turns AD CS from “a certificate server” into an operationally viable PKI. It allows domain-joined computers and users to automatically enroll and renew certificates based on template permissions.
Autoenrollment is configured via Group Policy:
For computer certificates: Computer Configuration → Policies → Windows Settings → Security Settings → Public Key Policies → Certificate Services Client – Auto-Enrollment.
For user certificates: User Configuration → Policies → Windows Settings → Security Settings → Public Key Policies → Certificate Services Client – Auto-Enrollment.
Enable autoenrollment and ensure “Renew expired certificates, update pending certificates, and remove revoked certificates” is selected.
Then, ensure the template security permissions include Autoenroll for the relevant principals (for example, “Domain Computers” for a machine authentication template, or a scoped group for user certificates).
This is where you benefit from earlier use-case scoping. If your first phase is server TLS certificates for internal services, you might restrict autoenrollment to a group like “TLS-Enabled Servers” rather than every computer account.
To force a client to evaluate autoenrollment without waiting for background refresh:
powershell
# On a client computer
gpupdate /force
certutil -pulse
On modern Windows, autoenrollment processing is integrated into policy refresh, but certutil -pulse remains a useful nudge.
A real-world scenario here is an IIS farm where nodes scale up and down. With autoenrollment, new nodes can receive the correct server authentication certificate automatically as they join the domain and land in the right OU or group. Without this, certificate deployment becomes a manual bottleneck and a frequent cause of expired cert outages.
Deploy templates for common enterprise scenarios
With CA hierarchy and autoenrollment working, you can now implement templates aligned to practical scenarios. The key is to keep template count small at first, and expand only when a distinct requirement appears.
Server authentication (TLS) for internal services
For internal web services, start by duplicating the “Web Server” template. Configure:
Subject Name: usually “Build from this Active Directory information” for domain-joined servers, and include DNS name in SAN.
EKU: Server Authentication.
Key usage: Digital Signature and Key Encipherment for RSA TLS.
Validity: often 1 year.
Security: allow enroll/autoenroll for a scoped group of server accounts.
If you need certificates for non-domain devices (appliances, Linux hosts without AD enrollment), you can still use AD CS but you’ll use manual enrollment or a different mechanism. Avoid weakening your enterprise template to accommodate exceptions; create a separate template and control who can use it.
Domain controller certificates for LDAPS
For LDAPS, domain controllers need certificates that include the correct server authentication EKU and the right subject/SAN entries. In many environments, the “Domain Controller Authentication” template is used, but you should verify it matches your needs and doesn’t include legacy EKUs you don’t want.
A practical approach is to:
Use a template intended for domain controllers.
Scope autoenrollment to Domain Controllers.
Ensure CDP/AIA reachability from clients that will use LDAPS.
This directly addresses the earlier scenario where an audit requires LDAPS. Once the template is published and autoenrollment enabled, DCs will enroll and renew automatically, avoiding annual scramble when certificates expire.
Client authentication for Wi-Fi/VPN (EAP-TLS)
EAP-TLS requires client certificates (user and/or computer) and a RADIUS/NPS server certificate. For clients, duplicate “User” and/or “Computer” templates and configure:
EKU: Client Authentication.
Subject name: built from AD; avoid allowing user-supplied subject.
Private key: mark as non-exportable for user certs in most cases.
Security: enroll/autoenroll for scoped groups.
For NPS, you’ll also issue a server authentication certificate with the correct DNS name clients use to reach the RADIUS server.
This use case is where revocation and availability become more visible. If a user leaves the company, you may revoke their certificate and expect access to drop promptly. That means your CRL/OCSP infrastructure must be reachable by NPS and any validating components.
Publish templates and verify issuance behavior
After you create a template, it isn’t active until you publish it on the issuing CA. In the Certification Authority console under Certificate Templates, choose “New” → “Certificate Template to Issue,” then select your template.
From a client or server, you can verify template availability and enrollment behavior. For example, on a server expected to receive a web server certificate, you can run:
powershell
# List CAs visible to the client
certutil -config - -ping
# Trigger enrollment evaluation
certutil -pulse
# Inspect issued certs
certlm.msc
For web servers, you’ll usually bind the issued certificate to IIS. While IIS binding is an application step, it’s worth standardizing how you select certificates: pick by thumbprint and automate bindings where possible, especially in farms.
If you’re integrating with load balancers or reverse proxies, decide where TLS terminates. If TLS terminates on a device that cannot autoenroll (or is not domain-joined), plan a separate issuance workflow, potentially including manual certificate requests with a tightly controlled template.
Configure CA auditing and logging for operational visibility
PKI is security infrastructure, so you want visibility into what is being issued, changed, and revoked.
Enable CA auditing to record events such as certificate issuance, revocation, and CA configuration changes. This is done in CA properties (Auditing tab) and also relies on Windows Security event log policies.
In addition to event logs, monitor:
CA database growth (the CA maintains an ESE database).
CRL publication success.
Service health and certificate enrollment errors.
Export and centralize CA logs to your SIEM if you have one. If you don’t, at least ensure logs are retained according to your security policy.
From an operational standpoint, this helps with incident response. If a certificate is suspected of misuse, you need to answer basic questions quickly: who requested it, from where, based on which template, and when.
Implement certificate revocation practices (and when OCSP is worth it)
Revocation is the process of marking a certificate as no longer valid before its expiration. Clients check revocation using CRLs (downloaded lists) or OCSP (online status checks).
In many internal TLS scenarios, revocation checking is inconsistent across clients and stacks. Some applications soft-fail if revocation endpoints are unreachable; others hard-fail. You should test the actual client behavior for your critical applications.
For authentication scenarios (EAP-TLS, smart card logon), revocation checking is typically more enforced. That’s why early planning for reachable CDPs matters.
OCSP via the Online Responder role can reduce bandwidth and speed up checks. It is especially useful when:
You have many endpoints validating frequently.
CRLs are large due to high issuance volume and revocations.
You need lower latency for auth flows (for example, Wi-Fi connections at scale).
If you implement OCSP, treat it like an availability component: redundant responders, stable DNS name, and monitoring. Also understand that OCSP responders themselves need certificates and rely on correct CA chain and AIA.
Back up the CA correctly (private keys, database, and configuration)
Backing up a CA is not just “system state.” You need:
The CA private key and certificate.
The CA database (issued certificates and requests).
The CA configuration/registry settings.
On Windows, the built-in CA backup can be performed from the Certification Authority console or via certutil.
powershell
# Example: backup CA database and private key (you will be prompted for a password)
certutil -backupDB D:\CABackup\DB
certutil -backupKey D:\CABackup\Key
Store backups securely, with access controls appropriate for tier-0 assets. If an attacker obtains your CA private key, they can mint trusted certificates.
Also consider restore testing. A backup you’ve never restored is a hope, not a plan. Schedule periodic restore drills in an isolated environment.
Manage renewal and lifecycle before it becomes urgent
Certificates expire, and CA certificates expire too. Many PKI outages are caused not by complex attacks but by neglected renewal planning.
Establish a lifecycle calendar:
Root CRL republish schedule (because the root is offline).
Issuing CA CRL republish schedule.
Issuing CA certificate renewal window (years out, but plan early).
End-entity renewal behavior (autoenrollment should renew well before expiration).
For the offline root, make CRL renewal a formal operational runbook item. If the root CRL expires, clients may fail chain validation depending on how strictly they enforce it.
A practical mini-case: an organization deploys EAP-TLS for Wi-Fi and everything works for six months, then connectivity starts failing intermittently on new devices. The issue turns out to be an expired CRL that devices attempted to fetch during authentication, causing revocation check failures. This kind of outage is preventable with a simple publication schedule and monitoring.
Integrate non-Windows systems thoughtfully
Even if your environment is “Windows-first,” you likely have Linux servers, network appliances, Java services, Kubernetes clusters, or SaaS integrations. AD CS can still be a central CA, but you must choose enrollment and trust distribution methods per platform.
For Linux, common approaches include:
Manual CSR generation (openssl) and submission to the CA via web enrollment (if enabled) or via an administrative workflow.
Using a certificate management agent that can integrate with Microsoft CA (often via custom workflows).
For appliances and load balancers, you typically generate CSRs on the device and have the CA sign them using a dedicated template that allows supply in the request. That template must be locked down so only authorized admins can enroll.
For trust, domain-joined Windows clients automatically trust enterprise roots via AD. Non-domain systems need the root (and often intermediate/issuing) CA certificates installed in their trust store. Publish the chain in a well-known internal location and treat that distribution as part of platform build standards.
This is where your earlier choice of stable AIA URLs helps: even non-domain clients can fetch issuing CA certificates if they’re missing, as long as they already trust the root.
Consider NDES/SCEP only when you actually need it
Some device classes (mobile devices, network gear, MDM-managed endpoints) use SCEP (Simple Certificate Enrollment Protocol). In AD CS, SCEP is provided through the Network Device Enrollment Service (NDES) role.
NDES can be useful, but it introduces additional security and operational complexity: registration authority behavior, challenge passwords, and a web-facing endpoint that must be protected. If your initial scope is domain-joined servers and users, you can postpone NDES.
If you do need it, treat NDES as an application tier:
Host it on a dedicated server.
Use TLS with a properly issued server certificate.
Restrict network access to only the MDM/management systems that require it.
Scope templates carefully and avoid issuing overly broad client authentication certificates to unmanaged devices.
Validate the PKI with chain building and real application tests
Once templates and autoenrollment are in place, validate at three layers: cryptographic chain, revocation reachability, and application behavior.
At the chain level, confirm that:
Clients can build from end-entity certificate → issuing CA → root CA.
AIA URLs are reachable and serve the correct issuing CA certificate.
At the revocation level, confirm that:
Clients can reach CRL distribution points.
CRLs are current and not close to expiration.
At the application level, test your actual use cases:
Bind a certificate to an IIS site and confirm clients can connect without revocation delays.
Enable LDAPS and confirm LDAP clients validate the certificate chain.
Configure NPS for EAP-TLS and validate with a test user and device.
Keep these tests in a living validation runbook. The environment will change—new subnets, VPN redesigns, DNS changes—and PKI tends to be the canary that reveals broken reachability.
A mini-case that illustrates why app-level testing matters: a team deploys a new internal Java service and imports the root CA into the JVM trust store but forgets the issuing CA chain. Some Java stacks don’t fetch intermediates from AIA automatically, so TLS fails until the intermediate is explicitly added. A validation checklist that includes “test from Java client” catches this early.
Operate AD CS safely: permissions, change control, and template hygiene
Once AD CS is issuing certificates, the biggest long-term risk often becomes template sprawl and permission drift. Every new template is another policy surface area that could be misconfigured.
To keep the system safe and manageable:
Limit who can create/modify templates. Template changes should be reviewed.
Avoid granting Enroll to large groups on templates that allow subject supply.
Regularly review issued certificates and template usage. Retire templates that aren’t used.
Keep CA administrators separate from domain administrators where feasible, and treat CA admin access as tier-0.
Also protect the CA itself:
Restrict inbound management access (RDP/WinRM) to admin networks.
Use credential guardrails (separate admin accounts, MFA via privileged access solutions where possible).
Monitor for unexpected certificate issuance volume spikes, which can be a sign of abuse.
If you ever need to revoke an issuing CA (for example, due to compromise), having the offline root design allows you to respond without rebuilding your trust anchor. That is the payoff of the earlier architecture work.
Reference deployment: a cohesive rollout plan you can execute
Putting the pieces together, a realistic rollout sequence for Active Directory Certificate Services looks like this:
Start with a design document that lists initial use cases, CA hierarchy (offline root + issuing), naming, crypto, validity, and revocation URLs. This ensures CDP/AIA are stable from the beginning.
Build the offline root CA, generate and publish its certificate and CRL to HTTP, and publish the root to AD trust stores.
Build the issuing CA, obtain its subordinate certificate from the root, and configure CDP/AIA to use your stable HTTP endpoints. Publish initial CRLs.
Create a minimal set of templates: one for server TLS, one for domain controllers (if LDAPS is in scope), and one for client auth (if EAP-TLS is in scope). Keep them scoped and avoid requester-supplied SAN unless required.
Enable autoenrollment via GPO for the OUs/groups in scope. Validate enrollment on pilot systems.
Run application-level pilots: one IIS service, one LDAPS test, one NPS EAP-TLS test. Expand scope gradually.
Establish operations: CRL publishing schedule, CA backups, monitoring, and template change control.
This plan aligns with the real-world scenarios described earlier: it supports mTLS/internal TLS at scale, makes LDAPS sustainable through automated DC certificates, and lays the groundwork for EAP-TLS without building unnecessary components.
By the time you reach steady-state, your PKI should feel boring: certificates enroll and renew automatically, revocation endpoints are reachable, templates are minimal and well governed, and CA keys are protected with the right level of administrative control. That “boring” outcome is exactly what secure communications infrastructure should look like.