Microsoft recently announced the general availability of its new PKI-as-a-Service platform called Microsoft Intune Cloud PKI. With Intune Cloud PKI, administrators create certification authorities (CAs) to issue and manage user and device authentication certificates for Intune-managed endpoints. Cloud PKI also provides hosted Authority Information Access (AIA) and Certificate Revocation List (CRL) Distribution Point (CDP) services, in addition to Simple Certificate Enrollment Protocol (SCEP) service, so administrators do not have to deploy on-premises infrastructure to take advantage of certificate-based authentication.
Certificate Templates
After deploying your Intune Cloud PKI root and issuing CAs, you may wonder where to find the associated certificate templates. If you are familiar with traditional on-premises Active Directory Certificate Services (AD CS) implementations, this is how you define the purpose, key policy, security parameters, and lifetime of the certificate issued using that template. However, Intune Cloud PKI does not use certificate templates in the traditional way many administrators are familiar with.
Note: Microsoft may introduce support for certificate templates for Intune Cloud PKI in the future. However, it is not supported at the time of this writing.
SCEP Profile
Administrators define certificate policies and security parameters using Intune’s SCEP device configuration profile instead of certificate templates. In essence, the SCEP profile functions as the certificate template. With the Intune device configuration profile, administrators can define the following settings.
Certificate Type
The certificate type can be either a user or a device. Intune Cloud PKI can issue certificates for either or both, as required.
Subject Name (User)
The subject name is unimportant for user authentication certificates because the User Principal Name (UPN) defined in the Subject Alternative Name field is used to authenticate the user. In this field, the administrator can use whatever they like. However, it’s common to use the username here. Avoid using the email attribute here because there’s no guarantee that every user will have this defined on the Active Directory (AD) user object.
Subject Name (Device)
Administrators should supply the device’s fully qualified domain name (FQDN) for device authentication certificates in the subject name field. For hybrid Entra joined devices, administrators can use the {{FullyQualifiedDomainName}} variable. For native Entra-joined devices, you can use {{DeviceName}} and append your DNS suffix, for example, {{DeviceName}}.corp.example.net.
Note: Intune supports numerous variables to populate fields for certificates. You can find a list of supported variables in the following locations.
User Certificate Variables: https://learn.microsoft.com/en-us/mem/intune/protect/certificates-profile-scep#create-a-scep-certificate-profile:~:text=Manager%20blog%20post.-,User%20certificate%20type,-Use%20the%20text
Device Certificate Variables: https://learn.microsoft.com/en-us/mem/intune/protect/certificates-profile-scep#create-a-scep-certificate-profile:~:text=on%20the%20device.-,Device%20certificate%20type,-Format%20options%20for
Subject Alternative Name (User)
The Subject Alternative Name (SAN) field for user authentication certificates should be populated with the User Principal Name (UPN) value. Ensure this value is appropriately configured internally and supports sign-in to AD.
Subject Alternative Name (Device)
The SAN field for device authentication certificates should be populated with the device’s FQDN. Follow the guidance for device subject names covered previously.
Certificate Validity Period
This field allows the administrator to define the certificate’s validity period. The best practice is to limit the lifetime to no more than one year. A shorter lifetime is recommended for certificates not backed by a Trusted Platform Module (TPM).
Key Storage Provider
This value is critical to ensuring integrity for issued user and device authentication certificates. The best practice is to select Enroll to Trusted Platform Module (TPM) KSP, otherwise fail. However, if you must issue certificates to endpoints without a TPM (e.g., legacy devices, virtual machines, etc.), consider a separate profile with a shorter certificate lifetime to limit exposure.
Key Usage
Digital signature and Key encipherment are required for user and device authentication certificates.
Key Size
The 2048-bit key size is the minimum recommended value for certificates with RSA keys. Using 4096-bit is not recommended for end-entity certificates and can potentially cause conflicts in some cases. Intune Cloud PKI does not support the 1024-bit key size.
Hash Algorithm
SHA-2 is the best practice for the hash algorithm. SHA-1 has been deprecated and should not be used.
Root Certificate
Select the Cloud PKI root CA certificate.
Extended Key Usage
The minimum requirement for user and device authentication certificates is Client Authentication (1.3.6.1.5.5.7.3.2).
Renewal Threshold
This value specifies at what point the certificate can be renewed. 20% is commonly used for certificates with a one-year lifetime.
SCEP Server URLs
This value can be found on the configuration properties page of your Cloud PKI issuing CA. The URI will include a variable in the URL. The variable is there by design. Copy and paste this URL exactly as displayed in the SCEP URL field.
Training
Are you interested in learning more about issuing and managing certificates with Microsoft Intune? Would you like to know how to securely and optimally implement PKCS and SCEP infrastructure on-premises? Do you want more details about deploying and managing Microsoft Intune Cloud PKI? Register now for my upcoming three-day live Certificates and Intune Masterclass training event at the ViaMonstra online training academy. We’ll deep-dive into all aspects of certificate management using Intune with on-premises AD CS and Intune Cloud PKI. I’ll be sharing many advanced techniques for adequately securing your certificate infrastructure. Space is limited, so register now!
Additional Information
Mastering Certificates with Intune Training Course
Microsoft Intune Cloud PKI Overview
Microsoft Intune Cloud PKI and Active Directory
Microsoft Intune Certificate Connector Failure
Microsoft Intune Certificate Connector Configuration Failed
Microsoft Intune Certificate Connector Configuration Failure
Microsoft Intune Certificate Connector Service Account and PKCS
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