Add an SSH Server With Certificate Auth and User Provisioning

Last modified on March 28, 2024


This guide describes how to add an SSH (Certificate Based with User Provisioning) resource in the Admin UI. This resource type uses certificates for authentication and uses Remote Identities to provision a local user with a home directory on the SSH server on each connection.

If you’d like to add a certificate-based SSH server without user provisioning, please see Add an SSH Server With Certificate Auth.


Before you begin, ensure that the following requirements are met.

  • The server you are attempting to add must be accessible from your StrongDM gateways or relays.
  • Remote Identities must be configured for users intending to connect.

Configure the Trusted CA

Review StrongDM CA public key

Every organization in StrongDM is automatically assigned a unique Certificate Authority (CA) for SSH, known as a Strong CA. The Strong CA is a cryptographic key pair in charge of issuing and validating certificates for every SSH session. You need to add the SSH CA public key as a trusted source on any hosts you want to access with this option.

How to view and copy the StrongDM SSH CA public key

  1. Log in to the StrongDM Admin UI.
  2. Go to Network > Certificate Authorities and select an SSH CA to use.
  3. From the SSH CA’s Settings tab, select one of the certificates shown, or create a new certificate.
  4. Click the i button beside the certificate’s fingerprint.
    StrongDM SSH Certificate Authority Page Showing Copy Button
    StrongDM SSH Certificate Authority Page Showing Copy Button
  5. From the SSH Certificate dialog that displays, use the Copy button to copy the SSH CA public key to your clipboard.
    Example SSH Certificate Dialog
    Example SSH Certificate Dialog

Add the CA to your host

The next step is to tell your host to trust certificates issued by your organization’s CA. If you have not already, add your organization’s SSH CA public key to the targeted host.

  1. Create a /etc/ssh/ file and add the SSH CA public key.

  2. SSH can sometimes be unpredictable if permissions are not set correctly. Therefore, update the file’s permissions:

    sudo chmod 600 /etc/ssh/
  3. With your editor of choice, modify /etc/ssh/sshd_config by appending the following lines:

    # StrongDM CA
    TrustedUserCAKeys /etc/ssh/
  4. Restart the SSH service on this host for the changes to take effect. Note that the command you execute may differ based on your system configuration, and you may need to restart sshd or ssh, as in the following example:

    sudo systemctl restart ssh

Configure Privileged User

A privileged user called strongdm must be configured on the server to perform the provisioning. This privileged user is allowed to authenticate with the certificate authority (CA).

  1. On the target server, create a privileged user called strongdm.
  2. Configure that user to use a restricted bash with access to the following:
    • useradd
    • usermod
    • userdel

Add a Certificate-Based SSH Server With User Provisioning in the Admin UI

To add your new SSH (Certificate Based with User Provisioning) server as a StrongDM resource, use the following steps.

  1. In the Admin UI, go to Infrastructure > Servers.
  2. Click Add server.
  3. For Server Type, select SSH (Certificate Based with User Provisioning).
  4. For Authentication, select Remote Identities and enter the healthcheck username, which is the username that will be utilized to verify StrongDM’s connection to the server.
  5. Set other required resource properties to configure how the StrongDM relay connects to the server via SSH.
  6. Click Create to save the resource.

Configuration is now complete.

After the server is created, the Admin UI displays that resource as unhealthy until the healthchecks run successfully. When the resource is ready, the Health icon indicates a positive, green status.

Resource properties

Configuration properties are visible when you add a Server Type or when you click to view the server’s settings. The following table describes the settings available for your SSH (Certificate Based with User Provisioning) server.

Display NameRequiredMeaningful name to display the resource throughout StrongDM; exclude special characters like quotes (") or angle brackets (< or >)
Server TypeRequiredSelect SSH (Certificate Based)
HostnameRequiredHostname or IP address to which you are connecting, such as; relay server should be able to connect to your target server or hostname
PortRequiredPort to connect to the resource; default port value 22
Bind InterfaceRead onlyAutomatically generated IP address value in the to IP address range; default is; preferred bind interface value can be modified later under Settings > Port Overrides
Port OverrideRead onlyAutomatically generated with a value between 1024 to 59999 as long as that port is not used by another resource; preferred port can be modified later under Settings > Port Overrides
Certificate AuthorityRequiredWhere the credentials for the server are stored; defaults to Strong CA; to learn more, see Certificate Authority options
Key TypeRequiredSigning algorithm with default value set to RSA-2048; other options include RSA-4096, ECDSA-256, ECDSA-384, ECDSA-521, and ED25519; to learn more, see Key Type options
AuthenticationRequiredSelect Leased Credentials (default) or Remote Identities
UsernameRequiredDisplays if Authentication is set to Leased Credentials; enter the username the relay should utilize to connect to the server via SSH (for example, bob.belcher)
Healthcheck UsernameRequiredDisplays if Authentication is set to Remote Identity; enter the username that will be utilized to verify StrongDM’s connection to the server; this username will be created on the server if it doesn’t already exist
Allow Port ForwardingOptionalWhen enabled, allows SSH connections proxied by StrongDM for this server to accept local forwarding requests; this checkbox is shown when the Allow port forwarding through SSH? option is turned on in the Admin UI security settings; see Port Forwarding for more information
Resource TagsOptionalResource tags consisting of key-value pairs <KEY>=<VALUE> (for example, env=dev)

Certificate Authority options

By default, server credentials are stored in Strong CA. If the Enterprise bundle is enabled for your organization, you may use a third-party CA, instead of the default Strong CA, to issue certificates for authentication to your certificate-based SSH resources.

For more information, please see Certificate Authorities.

Key type options

The following table describes the different key types StrongDM can use to encrypt and secure SSH connections.

Key typeDescriptionAdditional information
RSA-20482048-bit key generated with RSA algorithmLowest security guarantees, but has broad support across hosts
RSA-40964096-bit key generated with RSA algorithmSlightly better than RSA-2048; still uses RSA, but larger keys can prolong the time to crack if an attacker gains access
ECDSA-256Key generated with 256-bit elliptic curve and ECDSA algorithmProvides better security guarantees than RSA
ECDSA-384Key generated with 384-bit elliptic curve and ECDSA algorithmSlightly better than ECSDA-256
ECDSA-521Key generated with 521-bit elliptic curve and ECDSA algorithmServes as the best ECDSA choice from a security standpoint
ED25519Key generated with ED25519 algorithmProvides the best performance and comparable security to ECDSA; much smaller keys, but not as widely supported as other options

Connect to the Server

You can now connect to the server via SSH (for example, in the CLI, use sdm ssh <SERVER_DISPLAY_NAME>) and verify that a user is provisioned upon connection.

Once connected, you are logged in with the username that was set as the Remote Identity Username in your StrongDM user profile. That username did not exist previously—it was provisioned when the SSH session started. Moreover, if you specified a Remote Identity Role on your StrongDM user profile, your user is placed in a group with that same role name.

Additional Considerations

  • You may have an existing CA key pair and certificate to perform direct SSH or other tasks. You can continue to use this key pair, but you cannot import this CA into StrongDM.
  • You do not need to sign these keys, or any user keys. StrongDM handles that for you and for your users.
  • Session-based certificates for users are automatically renewed every 3 minutes.