Teleport SSO Authentication with GitLab

How to use GitLab as a single sign-on (SSO) provider with Teleport

This guide will cover how to configure GitLab to issue SSH credentials to specific groups of users. When used in combination with role based access control (RBAC), it allows administrators to define policies like:

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

Prerequisites

• At least two groups in GitLab with users assigned.
• Teleport role with access to maintaining oidc resources. This is available in the default editor role.

tsh login --proxy=teleport.example.com [email protected]
tctl status
Cluster  teleport.example.com
Version  12.1.1
CA pin   sha256:abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678

tsh login --proxy=myinstance.teleport.sh [email protected]
tctl status
Cluster  myinstance.teleport.sh
Version  12.1.1
CA pin   sha256:sha-hash-here

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

Configure GitLab

You should have at least one group configured in GitLab to map to Teleport roles. In this example we use the names gitlab-dev and gitlab-admin. Assign users to each of these groups.

1. Create a Application in one of your Groups that will allow using GitLab as a OAuth provider to Teleport.

Settings

• Redirect URL https://<proxy url>/v1/webapi/oidc/callback such as https://teleport.example.com:3080/v1/webapi/oidc/callback
• Check Confidential, openid, profile, and email.

2. Collect the Application ID and Secret in the Application

These will be used in the Teleport OIDC Auth Connector.

3. Confirm the GitLab Issuer Address

For GitLab cloud that is https://gitlab.com. That allows accessing the Open-ID configuration at https://gitlab.com/.well-known/openid-configuration. If you are self hosting that is likely another local address.

Configure Teleport

Create a OIDC Connector

Create a OIDC connector resource: Replace the Application ID and the Secret with the values from GitLab.

kind: oidc
metadata:
  name: gitlab
spec:
  claims_to_roles:
  - claim: groups
    roles:
    - admin
    value: gitlab-admin
  - claim: groups
    roles:
    - dev
    value: gitlab-dev
  client_id: Application_ID
  client_secret: Secret
  display: GitLab
  issuer_url: https://gitlab.com
  prompt: "none"
  redirect_url: https://teleport.example.com:3080/v1/webapi/oidc/callback
  scope:
  - email
version: v2

Create the connector using tctl tool:

tctl create oidc-connector.yaml

Create Teleport Roles

We are going to create 2 roles, privileged role admin who is able to login as root and is capable of administrating the cluster and non-privileged dev.

kind: role
version: v5
metadata:
  name: admin
spec:
  options:
    max_session_ttl: 24h
  allow:
    logins: [root]
    node_labels:
      "*": "*"
    rules:
      - resources: ["*"]
        verbs: ["*"]

The developer role:

kind: role
version: v5
metadata:
  name: dev
spec:
  options:
    max_session_ttl: 24h
  allow:
    logins: [ "{{email.local(external.email)}}", ubuntu ]
    node_labels:
      access: relaxed

• Devs are only allowed to login to nodes labelled with access: relaxed label.
• Developers can log in as ubuntu user
• Notice {{external.email}} login. It configures Teleport to look at "email" GitLab claim and use that field as an allowed login for each user. The email.local(external.trait) function will remove the @domain and just have the username prefix.
• Developers also do not have any "allow rules" i.e. they will not be able to see/replay past sessions or re-configure the Teleport cluster.

Create both roles on the auth server:

tctl create admin.yaml
tctl create dev.yaml

Testing

The Web UI will now contain a new button: "Login with GitLab". The CLI is the same as before:

tsh --proxy=teleport.example.com login

This command will print the SSO login URL (and will try to open it automatically in a browser).

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