OAuth2 / OIDC Authentication for SSH

This guide will explain how to configure an SSO provider using OpenID Connect (also known as OIDC) to issue SSH credentials to a specific groups of users. When used in combination with role based access control (RBAC) it allows SSH administrators to define policies like:

• Only members of "DBA" group can SSH into machines running PostgreSQL.
• Developers must never SSH into production servers.

Prerequisites

• Admin access to the SSO/IdP being integrated with users assigned to groups/roles.
• Teleport role with access to maintaining oidc resources. This is available in the default editor role.

• Make sure you can connect to Teleport. Log in to your cluster using tsh, then use tctl remotely:

  tsh login --proxy=teleport.example.com [email protected]
  tctl status
  Cluster  teleport.example.com
  Version  13.1.0
  CA pin   sha256:abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678

  You can run subsequent tctl commands in this guide on your local machine.

  For full privileges, you can also run tctl commands on your Auth Service host.

Enable default OIDC authentication

Configure Teleport to use OIDC authentication as the default instead of the local user database.

You can either edit your Teleport configuration file or create a dynamic resource.

auth_service:
  authentication:
    type: oidc

Identity Providers

Register Teleport with the external identity provider you will be using and obtain your client_id and client_secret. This information should be documented on the identity providers website. Here are a few links:

• Auth0 Client Configuration
• Google Identity Platform
• Keycloak Client Registration

Add your OIDC connector information to teleport.yaml. A few examples are provided below.

OIDC Redirect URL

OIDC relies on HTTP re-directs to return control back to Teleport after authentication is complete. The redirect URL must be selected by a Teleport administrator in advance.

If the Teleport web proxy is running on proxy.example.com host, the redirect URL should be https://proxy.example.com:3080/v1/webapi/oidc/callback

OIDC connector configuration

The next step is to add an OIDC connector to Teleport. The connectors are manipulated via tctl resource commands. To create a new connector, create a connector resource file in YAML format, for example oidc-connector.yaml.

The file contents are shown below. This connector requests the scope group from the identity provider then mapping the value to either to admin role or the user role depending on the value returned for group within the claims.

#
# Example resource for an OIDC connector
# We recommend using OIDC for G Suite, Auth0 and Keycloak
#
kind: oidc
version: v2
metadata:
  name: new_oidc_connector
spec:
  redirect_url: "https://<cluster-url>/v1/webapi/oidc/callback"
  client_id: <client id>
  # connector display name that will be appended to the title of "Login with"
  # button on the cluster login screen so it will say "Login with Google".
  # Teleport will provide custom CSS for 'Google'.
  display: Google
  client_secret: <client secret>
  issuer_url: https://<issuer-url>
  scope: [<scope value>]
  claims_to_roles:
    - {claim: "hd", value: "example.com", roles: ["editor"]}

Create the connector:

Log in to your cluster with tsh so you can use tctl from your local machine.
You can also run tctl on your Auth Service host without running "tsh login"
first.
tsh login --proxy=teleport.example.com --user=myuser
tctl create oidc-connector.yaml

Create Teleport Roles

The next step is to define Teleport roles. They are created using the same tctl resource commands as we used for the auth connector.

Below are two example roles that are mentioned above, the first is an admin with full access to the system while the second is a developer with limited access.

# role-admin.yaml
kind: "role"
version: "v3"
metadata:
  name: "admin"
spec:
  options:
    max_session_ttl: "90h0m0s"
  allow:
    logins: [root]
    node_labels:
      "*": "*"
    rules:
      - resources: ["*"]
        verbs: ["*"]

Users are only allowed to login to nodes labelled with access: relaxed teleport label. Developers can log in as either ubuntu to a username that arrives in their assertions. Developers also do not have any rules needed to obtain admin access.

# role-dev.yaml
kind: "role"
version: "v3"
metadata:
  name: "dev"
spec:
  options:
    max_session_ttl: "90h0m0s"
  allow:
    logins: [ "{{external.username}}", ubuntu ]
    node_labels:
      access: relaxed

Create both roles:

tctl create role-admin.yaml
tctl create role-dev.yaml

Optional: ACR Values

Teleport supports sending Authentication Context Class Reference (ACR) values when obtaining an authorization code from an OIDC provider. By default ACR values are not set. However, if the acr_values field is set, Teleport expects to receive the same value in the acr claim, otherwise it will consider the callback invalid.

In addition, Teleport supports OIDC provider specific ACR value processing which can be enabled by setting the provider field in OIDC configuration. At the moment, the only build-in support is for NetIQ.

A example of using ACR values and provider specific processing is below:

# example connector which uses ACR values
kind: oidc
version: v2
metadata:
  name: "oidc-connector"
spec:
  issuer_url: "https://oidc.example.com"
  client_id: "xxxxxxxxxxxxxxxxxxxxxxx.example.com"
  client_secret: "zzzzzzzzzzzzzzzzzzzzzzzz"
  redirect_url: "https://<cluster-url>:3080/v1/webapi/oidc/callback"
  display: "Login with Example"
  acr_values: "foo/bar"
  provider: netiq
  scope: [ "group" ]
  claims_to_roles:
     - claim: "group"
       value: "editor"
       roles: [ "editor" ]
     - claim: "group"
       value: "user"
       roles: [ "access" ]

Optional: Redirect URL and Timeout

The redirect URL must be accessible by all user, optional redirect timeout.

# Extra parts of OIDC yaml have been removed.
spec:
  redirect_url: https://<cluster-url>.example.com:3080/v1/webapi/oidc/callback
  # Optional Redirect Timeout.
  # redirect_timeout: 90s

Optional: Prompt

By default, Teleport will prompt end users to select an account each time they log in even if the user only has one account.

Teleport now lets Teleport Admins configure this option. Since prompt is optional, by setting the variable to none, Teleport will override the default select_account.

kind: oidc
version: v2
metadata:
  name: connector
spec:
  prompt: 'none'

The below example will prompt the end-user for reauthentication and will require consent from the client.

kind: oidc
version: v2
metadata:
  name: connector
spec:
  prompt: 'login consent'

A list of available optional prompt parameters are available from the OpenID website.

Optional: Disable email verification

By default, Teleport will validate the email_verified claim, and users who attempt to sign in without a verified email address will be prevented from doing so.

For testing and other purposes, you may opt out of this behavior by enabling allow_unverified_email in your OIDC connector. This option weakens the overall security of the system, so we do not recommend enabling it.

kind: oidc
version: v2
metadata:
  name: connector
spec:
  allow_unverified_email: true

Optional: Specify a claim to use as the username

By default, Teleport will use the user's email as their Teleport username.

You can define a username_claim to specify the claim that should be used as the username instead.

kind: oidc
version: v2
metadata:
  name: connector
spec:
  # Use the `preferred_username` claim as the user's Teleport username.
  username_claim: preferred_username

Testing

For the Web UI, if the above configuration were real, you would see a button that says Login with Example. Simply click on that and you will be re-directed to a login page for your identity provider and if successful, redirected back to Teleport.

For console login, you simple type tsh --proxy <proxy-addr> ssh <server-addr> and a browser window should automatically open taking you to the login page for your identity provider. tsh will also output a link the login page of the identity provider if you are not automatically redirected.

Troubleshooting

Troubleshooting SSO configuration can be challenging. Usually a Teleport administrator must be able to:

• Ensure that HTTP/TLS certificates are configured properly for both Teleport proxy and the SSO provider.

• Be able to see what SAML/OIDC claims and values are getting exported and passed by the SSO provider to Teleport.
• Be able to see how Teleport maps the received claims to role mappings as defined in the connector.

If something is not working, we recommend to:

• Double-check the host names, tokens and TCP ports in a connector definition.

Using the Web UI

If you get "access denied" or other login errors, the number one place to check is the Audit Log. You can access it in the Activity tab of the Teleport Web UI.

Example of a user being denied because the role clusteradmin wasn't set up:

{
  "code": "T1001W",
  "error": "role clusteradmin is not found",
  "event": "user.login",
  "method": "oidc",
  "success": false,
  "time": "2019-06-15T19:38:07Z",
  "uid": "cd9e45d0-b68c-43c3-87cf-73c4e0ec37e9"
}

Teleport does not show the expected Nodes

When Teleport's Auth Service receives a request to list Teleport Nodes (e.g., to display Nodes in the Web UI or via tsh ls), it only returns the Nodes that the current user is authorized to view.

For each Node in the user's Teleport cluster, the Auth Service applies the following checks in order and, if one check fails, hides the Node from the user:

• None of the user's roles contain a deny rule that matches the Node's labels.
• At least one of the user's roles contains an allow rule that matches the Node's labels.

If you are not seeing Nodes when expected, make sure that your user's roles include the appropriate allow and deny rules as documented in the Teleport Access Controls Reference.

When configuring SSO, ensure that the identity provider is populating each user's traits correctly. For a user to see a Node in Teleport, the result of populating a template variable in a role's allow.logins must match at least one of a user's traits.logins.

In this example a user will have usernames ubuntu, debian and usernames from the SSO trait logins for Nodes that have a env: dev label. If the SSO trait username is bob then the usernames would include ubuntu, debian, and bob.

kind: role
metadata:
  name: example-role
spec:
  allow:
    logins: ['{{external.logins}}', ubuntu, debian]
    node_labels:
      'env': 'dev'
version: v5