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Reverse proxy - Pomerium

You can secure your Jenkins application with JWT authentication and custom claims behind Pomerium, an open source reverse proxy.

Why use Pomerium with Jenkins?

You can set up role-based permissions in Jenkins to control a user’s privileges with Jenkins’ built-in authorization matrix. However, this method requires a username and password to sign in and relies on Jenkins’ user database to store credentials.

JWT authentication is a more secure method of identity verification that authenticates and authorizes users against an identity provider, eliminating the need to store or share credentials to access your Jenkins application.

However, Jenkins doesn’t support JWT authentication out of the box. With Pomerium, you can implement JWT authentication and apply claims to your route’s authorization policy to determine a user’s role and privileges before granting a user access to Jenkins.

Once you’ve configured JWT authentication, you can assign permissions within Jenkins for a specific user, any authenticated user, anonymous users, or a user group.

Secure Jenkins with Pomerium proxy

Note: This guide assumes v0.21 of Pomerium! Please refer to Pomerium’s guide on securing Jenkins for the latest version of this guide.

Before you begin

To complete this guide, you need:

  1. Docker and Docker Compose

  2. An identity provider (IdP)

If you haven’t, complete the Pomerium Core quickstart to familiarize yourself with running Pomerium in a container environment. It is free and should take no more than five minutes to get Pomerium open source proxy running.

Run Jenkins with Docker Compose

Create a project and add a file called docker-compose.yaml.

In the docker-compose.yaml file, add the following code:

jenkins:
  networks:
    main: {}
  image: jenkins/jenkins:lts-jdk11
  privileged: true
  user: root
  ports:
    - 8080:8080
    - 50000:50000

  volumes:
    # File path to Jenkins_home -- stores configs, build logs, and artifacts
    - ./home/jenkins_compose/jenkins_configuration:/var/jenkins_home
    # "sock" is the Unix socket the Docker daemon listens on by default
    - ./var/run/docker.sock:/var/run/docker.sock

Now, run docker compose up.

Set up your Jenkins instance

If your Jenkins container is set up correctly, the Setup Wizard guides you through several prompts before you can access your dashboard.

To set up your Jenkins instance:

  1. Go to localhost:8080 and enter the admin user password to continue. You can find the admin user password in your Docker logs or in /var/jenkins_home/secrets/initialAdminPassword.

  2. Install the suggested plugins

  3. Create an admin user. You can create your first admin user or select Skip and continue as admin. If you skip and continue as admin, the default username is admin and the password is the admin user password.

  4. In the Instance Configuration window, accept the default hostname

After completing the Setup Wizard prompts, you can access the Jenkins dashboard.

Now, run docker compose stop so you can configure Pomerium.

Configure Pomerium

Create a Pomerium configuration file

In your project’s root folder, create a config.yaml file.

In your config.yaml file, add the following code:

authenticate_service_url: https://authenticate.localhost.pomerium.io

idp_provider: REPLACE_ME
idp_provider_url: REPLACE_ME
idp_client_id: REPLACE_ME
idp_client_secret: REPLACE_ME

signing_key: REPLACE_ME

routes:
 - from: https://verify.localhost.pomerium.io
   to: http://verify:8000
   pass_identity_headers: true
   policy:
     - allow:
         and:
	email:
	      is: user@example.com
 - from: https://jenkins.localhost.pomerium.io
   to: http://jenkins:8080/
   host_rewrite_header: true
   pass_identity_headers: true
   policy:
     - allow:
         and:
           - domain:
               is: example.com
           - user:
               is: username

Next, you need to:

  • Update the identity provider configuration variables with your own

  • Replace user@example.com with the email associated with your IdP

  • Replace example.com with your organization’s domain name

  • Replace username with the username associated with your IdP

  • Generate a signing key

To generate a signing key, use the commands below:

# Generates a P-256 (ES256) signing key
openssl ecparam  -genkey  -name prime256v1  -noout  -out ec_private.pem
# Prints the base64 encoded value of the signing key
cat ec_private.pem | base64

Add the base64-encoded signing key to the signing_key variable in your config.yaml file.

Run Pomerium services with Docker Compose

In your docker-compose.yaml file, replace the code in the file with the Pomerium and Jenkins services below:

version: '3'
networks:
 main: {}
services:
 pomerium:
   image: pomerium/pomerium:latest
   volumes:
     - ./config.yaml:/pomerium/config.yaml:ro
   ports:
     - 443:443
   networks:
     main:
       aliases:
       - authenticate.localhost.pomerium.io
 verify:
   networks:
     main: {}
   image: pomerium/verify:latest
   expose:
     - 8000
 jenkins:
   networks:
     main: {}
   image: jenkins/jenkins:lts-jdk11
   privileged: true
   user: root
   ports:
     - 8080:8080
     - 50000:50000
   volumes:
     # File path to Jenkins_home -- stores configs, build logs, and artifacts
     - ./home/jenkins_compose/jenkins_configuration:/var/jenkins_home
     # "sock" is the Unix socket the Docker daemon listens on by default
     - ./var/run/docker.sock:/var/run/docker.sock

Run docker compose up and navigate to the external Jenkins route at https://jenkins.localhost.pomerium.io.

Jenkins will prompt you to sign in with your username and password. Sign in to continue to the Jenkins dashboard.

Install Jenkins plugins

Next, you need to add plugins to enable JWT authentication and bypass TLS validation.

Install the JWT Auth plugin:

  1. Select Manage Jenkins

  2. Under System Configuration, select Manage Plugins

  3. Select Available Plugins

  4. In the search bar, enter JWT Auth

  5. Select the JWT Auth plugin and Install without restart

Install the skip-certificate-check plugin:

  1. Select Available Plugins

  2. In the search bar, enter skip-certificate-check

  3. Select the skip-certificate-check plugin and Install without restart

Once you’ve installed both plugins, stop your containers.

Configure JWT authentication

Go to your external Jenkins route.

To configure JWT authentication:

  1. Go to Manage Jenkins

  2. Under Security, select Configure Global Security

  3. Under Authentication > Security Realm, select JWT Header Authentication Plugin

Under Global JWT Auth Settings, you’ll see form fields where you can enter JWT claims. Pomerium forwards a user’s associated identity information in a signed attestation JWT that’s included in upstream requests in an X-Pomerium-Jwt-Assertion header.

With the JWT Auth plugin installed, Jenkins can receive and parse the assertion header to authenticate users – you just need to give it the right instructions to find the header and JWT claims.

Enter the following information in the Global JWT Auth Settings field:

Table 1. Global JWT Auth Settings
Field Value

Header name

x-pomerium-jwt-assertion

Username claim name

name or email

Groups claim name

groups

Groups claim list separator

,

Email claim name

email

Acceptable issuers

authenticate.corp.example.com

Acceptable audiences

jenkins.corp.example.com

JWKS JSON URL

https://jenkins.corp.example.com/.well-known/pomerium/jwks.json

Note the following details about the fields above:

  • Username claim name can be either your name or email

  • Acceptable issuers must be the URL of the authentication domain that issued the JWT. The iss claim tells the target application who the issuing authority is and provides context about the subject.

  • Acceptable audiences must be the URL of the target application. The aud claim defines what application the JWT is intended for.

  • JWKS JSON URL appends /.well-known/pomerium/jwks.json to the external route URL. The JWKS endpoint provides Jenkins the user’s public key to verify their JWT signature.

You can go to the external verify route defined in your policy to view your JWT claims.

In the Authorization dropdown, configure Jenkins permissions so that Anonymous has Administer privileges.

  1. Select Matrix-based security

  2. Under Overall, assign Administer to Anonymous and Authenticated Users

If JWT authentication doesn’t authenticate you successfully, Jenkins signs you in as an anonymous user. With administer privileges, you can troubleshoot JWT settings as an anonymous user and try again.

Select save to apply the security settings.

Test JWT authentication

Restart your container. If the JWT authentication worked, your name appears in the dashboard instead of admin. To see more details about the request, add /whoAmI to the URL. For example, https://jenkins.localhost.pomerium.io/whoAmI.

Update your Jenkins authorization settings

Now, you can configure your Jenkins authorization settings:

  1. Select Matrix-based security

  2. Select Add user… and enter the name or email associated with your IdP (the value depends on what claim you entered for Username claim name)

Assign yourself Administer privileges and whatever privileges seem appropriate to Authenticated Users and Anonymous users.

Select save to apply the security changes.

Next steps: Add more context to your policies

You can adjust the authorization policy within Jenkins to limit or broaden what privileges authenticated and anonymous users have, but you can also extend your authorization policies with Pomerium.

For example:

  • You can build a policy that only allows users to access Jenkins at certain times of day or days of the week, or limit access to certain devices

  • You can import custom groups claims from your IdP and only allow access to members of the group

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