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Version: 19.x (unreleased)

Headless Authentication

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Headless Authentication provides a secure way to authenticate with Teleport on a machine that does not have the ability to authenticate directly with the required mechanisms.

For example:

  • Authenticating with WebAuthn or SSO MFA from a remote dev box
  • Authenticating with WebAuthn on a machine without a WebAuthn-compatible browser
  • Authenticating with SSO MFA from a browser that is not supported by your SSO provider
Headless Authentication Support

Headless Authentication only supports the following tsh commands:

  • tsh ls
  • tsh ssh
  • tsh scp

In the future, Headless Authentication will be extended to other tsh commands.

How it works​

In the Headless Authentication flow, a user on a remote machine requests headless authentication when running tsh commands. tsh sends a request to an API path on the Teleport Proxy Service, /webapi/login/headless, and the Teleport Proxy Service sends a request to the Teleport Auth Service to store a headless authentication request on its backend. tsh then obtains the ID of the request and prints a URL containing the ID in the user's terminal. The user accesses the URL on their browser and completes an MFA flow with the Teleport Auth Service.

Once the Teleport Auth Service authenticates the user, tsh generates a new private key in memory, and shares its public key only to obtain user certificates. tsh then holds user certificates in memory with a one-minute TTL to reduce the impact of exfiltration.

Prerequisites​

Step 1/3. Configuration​

A Teleport cluster capable of WebAuthn or SSO MFA is automatically capable of Headless Authentication without any additional configuration.

Optional: make Headless Authentication the default auth connector

To make Headless Authentication the default authentication method for your Teleport Cluster, add connector_name: headless to your cluster configuration.

Create a cap.yaml file or get the existing configuration using tctl get cluster_auth_preference:

kind: cluster_auth_preference
version: v2
metadata:
  name: cluster-auth-preference
spec:
  type: local
  second_factors: ["webauthn"]
  webauthn:
    rp_id: example.com
  connector_name: headless # headless by default

Update the configuration:

tctl create -f cap.yaml
cluster auth preference has been updated
Alternative: disable Headless Authentication

Headless Authentication is enabled automatically when WebAuthn or SSO MFA is configured. If you want to forbid Headless Authentication in your cluster, add headless: false to your configuration.

Create a cap.yaml file or get the existing configuration using tctl get cluster_auth_preference:

kind: cluster_auth_preference
version: v2
metadata:
  name: cluster-auth-preference
spec:
  type: local
  second_factors: ["webauthn"]
  webauthn:
    rp_id: example.com
  headless: false # disable Headless Authentication

Update the configuration:

tctl create -f cap.yaml
cluster auth preference has been updated

Step 2/3. Initiate Headless Authentication​

Run a headless tsh command with the --headless flag. This will initiate headless authentication, printing a URL and tsh command.

tsh ls --headless --proxy=proxy.example.com --user=alice
Complete headless authentication in your local web browser:
https://proxy.example.com:3080/web/headless/86172f78-af7c-5935-a7c1-ed06b94f17dc
or execute this command in your local terminal:
tsh headless approve --user=alice --proxy=proxy.example.com 86172f78-af7c-5935-a7c1-ed06b94f17dc

Step 3/3. Approve Headless Authentication​

To approve the headless authentication, click or copy+paste the URL printed by tsh in your local web browser. You will be prompted to approve the log in with MFA verification. Once approved, your initial tsh --headless <command> should continue as if you had logged in locally.

Unlike a standard login session, headless sessions are only available for the lifetime of a single tsh request. This means that for each tsh --headless command, you will need to go through the Headless Authentication flow:

Example: Listing SSH servers​

tsh ls --headless --proxy=proxy.example.com --user=alice
Complete headless authentication in your local web browser:
https://proxy.example.com:3080/web/headless/86172f78-af7c-5935-a7c1-ed06b94f17dc
or execute this command in your local terminal:
tsh headless approve --user=alice --proxy=proxy.example.com 86172f78-af7c-5935-a7c1-ed06b94f17dc
# User approves through link
Node Name Address        Labels
--------- -------------- -----------
server01  127.0.0.1:3022 arch=x86_64

Example: Initiating an SSH session​

tsh ssh --headless --proxy=proxy.example.com --user=alice alice@server01
Complete headless authentication in your local web browser:
https://proxy.example.com:3080/web/headless/864cccd9-2425-46d9-a9f2-636387e66ebf
or execute this command in your local terminal:
tsh headless approve --user=alice --proxy=proxy.example.com 864cccd9-2425-46d9-a9f2-636387e66ebf
# User approves through link and a ssh terminal starts
alice@server01 $
note

The Teleport user, --user parameter, is the Teleport user requesting Headless Authentication activity. If no --user parameter or environment variables set the OS user in the machine terminal is used.

The login username, --login parameter or login@hostname, for tsh ssh commands is the user to open a SSH session as. If no login username for the SSH session is set the OS terminal username is used. A Teleport user must have access to that login user for that server or they will receive an access denied message. The user could receive an access denied message after being approved for their Headless Authentication activity since the same access rights are granted or denied as if running from your local terminal.

Optional: Teleport Connect​

Teleport Connect can also be used to approve Headless Authentication logins. Teleport Connect will automatically detect the Headless Authentication login attempt and allow you to approve or cancel the request.

You will be prompted to tap your MFA key to complete the approval process.

Troubleshooting​

"WARN: Failed to lock system memory for headless login: ..."​

When using Headless Authentication, tsh does not write private key and certificate data to disk(~/.tsh). Instead, tsh holds these secrets in memory for the duration of the request. Additionally, it will try to lock the process memory to further protect the secrets from being stolen by other users on a shared machine.

Below are some of the specific warning messages you may run into and how to fix them:

"operation not permitted" OR "cannot allocate memory"​

In order to lock the process memory, your OS user must have permission to lock the amount of memory needed. Use ulimit -l to check your OS user's current limit. The exact amount of memory needed may vary from system to system, so we recommend updating your ulimit to unlimited, with either ulimit -l unlimited or by adding the line <os_username> hard memlock unlimited to your /etc/security/limits.conf.

"memory locking is not supported on non-linux operating systems"​

The mlockall syscall is only supported on Linux operating systems. This means that on other operating systems, the memory lock attempt will always fail and output the warning. We recommend only using Headless Authentication on Linux machines for the best level of security on shared machines.

Disable mlock​

If the above solutions are not feasible in your environment, you can also disable the memory locking requirement by setting the --mlock flag or TELEPORT_MLOCK_MODE environment variable to off or best_effort. This is not recommended in production environments on shared systems where a memory swap attack is possible.