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Configuring Headscale to use OIDC authentication

In order to authenticate users through a centralized solution one must enable the OIDC integration.

Known limitations:

No dynamic ACL support
OIDC groups cannot be used in ACLs

Basic configuration

In your config.yaml, customize this to your liking:

oidc:
  # Block further startup until the OIDC provider is healthy and available
  only_start_if_oidc_is_available: true
  # Specified by your OIDC provider
  issuer: "https://your-oidc.issuer.com/path"
  # Specified/generated by your OIDC provider
  client_id: "your-oidc-client-id"
  client_secret: "your-oidc-client-secret"
  # alternatively, set `client_secret_path` to read the secret from the file.
  # It resolves environment variables, making integration to systemd's
  # `LoadCredential` straightforward:
  #client_secret_path: "${CREDENTIALS_DIRECTORY}/oidc_client_secret"

  # Customize the scopes used in the OIDC flow, defaults to "openid", "profile" and "email" and add custom query
  # parameters to the Authorize Endpoint request. Scopes default to "openid", "profile" and "email".
  scope: ["openid", "profile", "email", "custom"]
  # Optional: Passed on to the browser login request – used to tweak behaviour for the OIDC provider
  extra_params:
    domain_hint: example.com

  # Optional: List allowed principal domains and/or users. If an authenticated user's domain is not in this list,
  # the authentication request will be rejected.
  allowed_domains:
    - example.com
  # Optional. Note that groups from Keycloak have a leading '/'.
  allowed_groups:
    - /headscale
  # Optional.
  allowed_users:
    - alice@example.com

  # If `strip_email_domain` is set to `true`, the domain part of the username email address will be removed.
  # This will transform `first-name.last-name@example.com` to the user `first-name.last-name`
  # If `strip_email_domain` is set to `false` the domain part will NOT be removed resulting to the following
  # user: `first-name.last-name.example.com`
  strip_email_domain: true

Azure AD example

In order to integrate Headscale with Azure Active Directory, we'll need to provision an App Registration with the correct scopes and redirect URI. Here with Terraform:

resource "azuread_application" "headscale" {
  display_name = "Headscale"

  sign_in_audience = "AzureADMyOrg"
  fallback_public_client_enabled = false

  required_resource_access {
    // Microsoft Graph
    resource_app_id = "00000003-0000-0000-c000-000000000000"

    resource_access {
      // scope: profile
      id   = "14dad69e-099b-42c9-810b-d002981feec1"
      type = "Scope"
    }
    resource_access {
      // scope: openid
      id   = "37f7f235-527c-4136-accd-4a02d197296e"
      type = "Scope"
    }
    resource_access {
      // scope: email
      id   = "64a6cdd6-aab1-4aaf-94b8-3cc8405e90d0"
      type = "Scope"
    }
  }
  web {
    # Points at your running Headscale instance
    redirect_uris = ["https://headscale.example.com/oidc/callback"]

    implicit_grant {
      access_token_issuance_enabled = false
      id_token_issuance_enabled = true
    }
  }

  group_membership_claims = ["SecurityGroup"]
  optional_claims {
    # Expose group memberships
    id_token {
      name = "groups"
    }
  }
}

resource "azuread_application_password" "headscale-application-secret" {
  display_name          = "Headscale Server"
  application_object_id = azuread_application.headscale.object_id
}

resource "azuread_service_principal" "headscale" {
  application_id = azuread_application.headscale.application_id
}

resource "azuread_service_principal_password" "headscale" {
  service_principal_id = azuread_service_principal.headscale.id
  end_date_relative    = "44640h"
}

output "headscale_client_id" {
  value = azuread_application.headscale.application_id
}

output "headscale_client_secret" {
  value = azuread_application_password.headscale-application-secret.value
}

And in your Headscale config.yaml:

oidc:
  issuer: "https://login.microsoftonline.com/<tenant-UUID>/v2.0"
  client_id: "<client-id-from-terraform>"
  client_secret: "<client-secret-from-terraform>"

  # Optional: add "groups"
  scope: ["openid", "profile", "email"]
  extra_params:
    # Use your own domain, associated with Azure AD
    domain_hint: example.com
    # Optional: Force the Azure AD account picker
    prompt: select_account

Google OAuth Example

In order to integrate Headscale with Google, you'll need to have a Google Cloud Console account.

Google OAuth has a verification process if you need to have users authenticate who are outside of your domain. If you only need to authenticate users from your domain name (ie @example.com), you don't need to go through the verification process.

However if you don't have a domain, or need to add users outside of your domain, you can manually add emails via Google Console.

Steps

Go to Google Console and login or create an account if you don't have one.
Create a project (if you don't already have one).
On the left hand menu, go to APIs and services -> Credentials
Click Create Credentials -> OAuth client ID
Under Application Type, choose Web Application
For Name, enter whatever you like
Under Authorised redirect URIs, use https://example.com/oidc/callback, replacing example.com with your Headscale URL.
Click Save at the bottom of the form
Take note of the Client ID and Client secret, you can also download it for reference if you need it.
Edit your headscale config, under oidc, filling in your client_id and client_secret:

oidc:
  issuer: "https://accounts.google.com"
  client_id: ""
  client_secret: ""
  scope: ["openid", "profile", "email"]

You can also use allowed_domains and allowed_users to restrict the users who can authenticate.

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