docs: update CA import instructions for HSMs (#51530)

Now that #51301 is merged, we have the ability to get all of the
active user CA certificates.

docs/pages/enroll-resources/desktop-access/active-directory.mdx

@@ -237,7 +237,7 @@ You must repeat these steps if you rotate the Teleport user certificate authorit
 
 To export the Teleport user CA certificate:
 
-1. Log on to a Windows domain controller where you can access **Group Policy Management**.
+1. Log on to a Windows host where you can access **Group Policy Management**.
 
 1. Open PowerShell and download the Teleport user certificate authority by running the following
    command and replacing `teleport.example.com` with the address of your Teleport cluster:
@@ -246,7 +246,11 @@ To export the Teleport user CA certificate:
    $ curl.exe -fo user-ca.cer https://<Var name="teleport.example.com"/>/webapi/auth/export?type=windows
    ```
 
-1. Take note of the path to the `user-ca.cer` file for use in a later step.
+   If you are using Teleport's support for HSM-backed keys, then your Teleport
+   cluster has multiple user CAs (one for each Auth Service instance). You can
+   download a bundle containing all CAs by appending `&format=zip` to the URL.
+
+1. Take note of the path to file you just downloaded for use in a later step.
 
 #### Create the GPO for the Teleport certificate
 
@@ -289,6 +293,8 @@ To configure the group policy object:
    ![Import Teleport CA](../../../img/desktop-access/ca.png)
    </Figure>
 
+   If you are using HSM-backed keys, you should repeat this step for each CA certificate.
+
 1. To ensure your GPO update takes effect immediately on this host,
    open PowerShell and run the following command (optional):
 
@@ -314,6 +320,9 @@ To publish the Teleport certificate in the Active Directory domain:
    This command enables the domain controllers to trust the Teleport CA so that
    certificate-based smart card authentication through Teleport can succeed.
 
+   If you are using HSM-backed keys, you should repeat this step for each CA certificate
+   in the zip file you exported earlier in this guide.
+
 #### Publish the Teleport CA to the NTAuth Store
 
 For authentication with Teleport-issued certificates to succeed, the
@@ -322,6 +331,9 @@ Teleport periodically publishes its CA after it is able to authenticate, but
 this step must be performed manually the first time for Teleport to have LDAP
 access.
 
+If you are using HSM-backed keys, you should repeat these steps for each CA certificate
+in the bundle.
+
 To publish the Teleport CA to LDAP:
 
 1. Open PowerShell and run the following command using the path to the `user-ca.cer`

docs/pages/enroll-resources/desktop-access/getting-started.mdx

@@ -48,6 +48,10 @@ To prepare a Windows computer:
    $ curl.exe -fo teleport.cer https://<Var name="teleport.example.com"/>/webapi/auth/export?type=windows
    ```
 
+   If you are using Teleport's support for HSM-backed keys, then your Teleport cluster
+   has multiple user CAs (one for each Auth Service instance). You can download a bundle
+   containing all CAs by appending `&format=zip` to the URL.
+
 3. Download the Teleport Windows Auth setup program:
 
 ```code
@@ -55,7 +59,11 @@ $ curl.exe -fo teleport-windows-auth-setup-v(=teleport.version=)-amd64.exe https
 ```
 
 4. Double-click the executable you downloaded to run the Teleport Windows Auth Setup program
-interactively and select the Teleport certificate that you exported when prompted.
+   interactively and select the Teleport certificate that you exported when prompted.
+
+   If you are using Teleport's support for HSM-backed keys and you downloaded a zip file in step 2,
+   then you should extract the zip file and repeat the process below for each CA certificate.
+   You can defer the reboot until you have installed all of the certificates.
 
    The setup program: