SCEPmanClient

SCEPmanClient is a PowerShell module intended to interact with SCEPmans REST API. Being platform independent and compatible with Windows PowerShell v5, you can use this module to request certificates for all use cases the REST API can be used for:

• Automatic issuance of server certificates

• Client certificates for unmanaged devices

• Enrollment of certificates to Linux devices

Installation

The SCEPmanClient module is available from the PowerShell Gallery and can be installed using the following command:

Install-Module -Name SCEPmanClient

Prerequisites

For the module to be functioning as expected you will need to add a small modification to your SCEPman deployment:

1

Add Home page URL

Add SCEPman's App Service URL: Navigate to the Branding & Properties section of the app registration. Add SCEPman's App Service URL to the Home page URL field:

This is required for the module to be able to automatically look up the App Registrations client id that is needed for access token retrieval.

2

Allow Azure PowerShell to interact with the App Registration

In the App Registration, navigate to Expose an API and create a custom scope that can be used to authorize the client Id 1950a258-227b-4e31-a9cf-717495945fc2 (Microsoft Azure PowerShell)

After creating an API scope, the Azure PowerShell application can be authorized:

3

Enable EST endpoint

Configuration

Required for certificate renewal

Configure your SCEPman App Service to accept mTLS client certificates. In the Configuration blade of the Settings section, verify that the Client certificate mode in Incoming client certificates is set to Optional.

Do not set the Client certificate mode to Require or Allow, as that would break normal operation of SCEPman on the SCEP endpoints!

Environment Variables

In order to make use of this scenario, you must set the following Environment Variables on the SCEPman app service.

AppConfig:DbCSRValidation:Enabled

Required for certificate enrollment and renewal

Set this variable to true to enable the validation of certificate signing requests (CSRs).

AppConfig:DbCSRValidation:AllowRenewals

Required for certificate renewal

Set this variable to true to enable certificate renewals.

AppConfig:DbCSRValidation:ReenrollmentAllowedCertificateTypes

Required for certificate renewal

Set this variable to a comma separated list of certificate types that you want to allow the renewal. See the linked variable documentation for a list of possible certificate types.

Example: Static,IntuneUser,IntuneDevice

Permissions

SCEPman has different roles that will allow different kinds of certificates to be enrolled. You can assign those in the SCEPman-api (default name) Enterprise Application:

CSR DB Requesters

This role is only assignable to service principals (App Registrations for example) by default and allows to request certificates with arbitrary subjects and usages.

CSR Self Service

This role can be assigned to users and will allow certificates to be enrolled with the following restrictions:

• Only ClientAuth EKU

• User certificates need to match the users UPN in either the subject or UPN subject alternative name

• Device certificates need to have a subject or SAN that SCEPman can map to a device object owned by the authenticated user

Usage Examples

Use Azure Authentication

Interactive Authentication

When requesting a new certificate without specifying the authentication mechanism, the user will be authenticated interactively by default. By using the -SubjectFromUserContext parameter, the certificate's subject and UPN SAN will be automatically populated based on the logged-in user's context:

New-SCEPmanCertificate -Url 'scepman.contoso.com' -SubjectFromUserContext -SaveToStore CurrentUser

Device Login

If you want to request a new certificate on a system without any desktop environment you can use the -DeviceCode parameter to perform the actual authentication on another session:

New-SCEPmanCertificate -Url 'scepman.contoso.com' -DeviceCode -SubjectFromUserContext -SaveToFolder /home/user/certificates

Service Principal Authentication

In fully automated scenarios an App Registration can be used for authentication. Inferring the subject from the authenticated context will not be possible in this case.

Parameter splatting will also make the execution more readable:

$Parameters = @{
    'Url'              = 'scepman.contoso.com'
    'ClientId'         = '569fbf51-aa63-4b5c-8b26-ebbcfcde2715'
    'TenantId'         = '8aa3123d-e76c-42e2-ba3c-190cabbec531'
    'ClientSecret'     = 'csa8Q~aVaWCLZTzswIBGvhxUiEvhptuqEyJugb70'
    'Subject'          = 'CN=WebServer'
    'DNSName'          = 'Webserver.domain.local'
    'ExtendedKeyUsage' = 'ServerAuth'
    'SaveToStore'      = 'LocalMachine'
}

New-SCEPmanCertificate @Parameters

Authenticate using certificates

Once a certificate has been issued using an authenticated context we can use it to renew it without providing any context again.

CertificateBySubject

Interacting with keystores is only possible on Windows

When providing the CertificateBySubject parameter, the module will automatically try find a suitable certificate for renewal in the CurrentUser and LocalMachine keystores.

The entered value will be regex matched against the subjects in all available certificates.

New-SCEPmanCertificate -CertificateBySubject 'WebServer' -SaveToStore 'LocalMachine'

Provide a specific certificate

$Certificate = Get-ChildItem Cert:\LocalMachine\My | Where-Object Thumbprint -eq '9B08EA68B16773CEF3C49D5D95BE50B784638984'

New-SCEPmanCertificate -Certificate $Certificate -SaveToStore LocalMachine

CertificateFromFile

On Linux systems a certificate renewal can be performed by passing the paths of an existing certificate and its private key.

New-SCEPmanCertificate -CertificateFromFile '~/certs/myCert.pem' -KeyFromFile '~/certs/myKey.key' -SaveToFolder '~/certs'

When using an encrypted private key you will asked for the password. You can also directly pass the keys password using the PlainTextPassword parameter.

Using SCEPman with a Azure Web Application Firewall

With SSL Profiles enabled, the WAF will terminate the TLS connections. This will in turn break certificate renewals using EST as the procedure relies on mTLS for authentication. In this case the UseSCEPRenewal parameter can be used to instead perform a certificate renewal complying with the SCEP protocol.

New-SCEPmanCertificate -CertificateBySubject 'WebServer' -SaveToStore 'LocalMachine' -UseSCEPRenewal

Please note that this requires additional SCEPman configuration regarding the static SCEP endpoint:

• AppConfig:StaticValidation:Enabled : true

• AppConfig:StaticValidation:AllowRenewals : true

• AppConfig:StaticValidation:ReenrollmentAllowedCertificateTypes: Static (Depending on the types intended for renewal)