Pomerium

# Programmatic access

This page describes how to obtain Pomerium access credentials programmatically via a web-based oauth2 style authorization flow. If you have ever used Google's gcloud commandline app, the mechanism is very similar.

# Components

# Login API

The API returns a cryptographically signed sign-in url that can be used to complete a user-driven login process with Pomerium and your identity provider. The login API endpoint takes a pomerium_redirect_uri query parameter as an argument which points to the location of the callback server to be called following a successful login.

Here's a full example.

# we'll call the hidden pomerium path below against a proxied-by-pomerium
# service, like our verify app below
ANY_POMERIUM_PROXIED_SERVICE=verify.example.com

# the service we're developing locally, this needs to be localhost to work with
# `pomerium_redirect_uri`, see **NOTE** below, to override this default
MY_LOCAL_DEV_SERVICE=http://localhost:8000

# create a request to the pomerium-proxied service
# `/.pomerium/...` is available for any proxied service
curl "https://$ANY_POMERIUM_PROXIED_SERVICE/.pomerium/api/v1/login?pomerium_redirect_uri=$MY_LOCAL_DEV_SERVICE"

# will output a URL like:
# https://authenticate.example.com/.pomerium/sign_in?pomerium_redirect_uri=http%3A%2F%2Flocalhost%3Fpomerium_callback_uri%3Dhttps%253A%252F%verify.example.com%252F.pomerium%252Fapi%252Fv1%252Flogin%253Fpomerium_redirect_uri%253Dhttp%253A%252F%252Flocalhost&sig=hsLuzJctmgsN4kbMeQL16fe_FahjDBEcX0_kPYfg8bs%3D&ts=1573262981

# open url above in a browser and you'll get redirected in the browser to
# > http://$MY_LOCAL_DEV_SERVICE/?pomerium_jwt=a.real.jwt or expanded as
# http://localhost:8000/?pomerium_jwt=programmatic.pomerium.jwt

# you can now use the value from `pomerium_jwt` to Authorize to our proxied endpoint (which you could use to proxy `localhost`)

curl -H 'Authorization: Pomerium a.real.jwt' https://verify.example.com
  • service.example.com is our endpoint fronted by pomerium-proxy
  • localhost:8000 is our service we're developing locally, it'll need to accept the programmatic token directly as a query param ?pomerium_jwt=programmatic.pomerium.jwt see callback handler
  • authenticate.example.com is the pomerium-authenticate service, we'll open that in the browser to authenticate, it will be set as iss on the jwt

Note: By default only localhost URLs are allowed as the pomerium_redirect_uri. This can be customized with the programmatic_redirect_domain_whitelist option.

# Alternative to Login API for localhost development

Alternatively you can create a new policy to route an endpoint to a bastion host (opens new window). You should include a HTTP proxy on this bastion host for HTTPS traffic. Here's one way to do it with nginx: https://jerrington.me/posts/2019-01-29-self-hosted-ngrok.html (opens new window) An HTTP proxy on the bastion allows us to receive HTTPS traffic with a self signed cert through LetsEncrypt.

This alternative will allow you to act as if your service is deployed and fronted by Pomerium. We will then forward the remote port from the bastion host behind the pomerium-proxy to localhost.

This is useful if you're using pass_identity_headers in your policy.

For example:

# a policy like
- from: https://my-dev-endpoint.example.com
  to: https://my-bastion-host.example.com:5000
  pass_identity_headers: true

Once this policy is applied and deployed, you can then forward the remote port of the HTTP proxy running on the bastion host that in this case proxies 5000 to 5001 internally.

We then forward the remote port from the bastion's HTTP proxy (5001) to localhost:8000, with an ssh tunnel like:

ssh -N -R 5001:localhost:8000 my-user@my-bastion-host.example.com

You can then go to https://my-dev-endpoint.example.com and have the pomerium-proxy route traffic securely to the bastion host and back through the ssh-tunnel, the headers and anything pomerium-proxy is setup to do to the request will be included in the forwarded request and traffic.

# Callback handler

It is the script or application's responsibility to create a HTTP callback handler. Authenticated sessions are returned in the form of a callback (opens new window) from pomerium to a HTTP server. This is the pomerium_redirect_uri value used to build login API's URL, and represents the URL of a (usually local) HTTP server responsible for receiving the resulting user session in the form of pomerium_jwt query parameters.

See the python script below for example of how to start a callback server, and store the session payload.

# Handling expiration and revocation

Your script or application should anticipate the possibility that your underlying refresh_token may stop working. For example, a refresh token might stop working if the underlying user changes passwords, revokes access, or if the administrator removes rotates or deletes the OAuth Client ID.

# High level workflow

The application interacting with Pomerium must manage the following workflow. Consider the following example where a script or program desires delegated, programmatic access to the domain verify.corp.domain.example:

  1. The script or application requests a new login url from the pomerium managed endpoint (e.g. https://verify.corp.domain.example/.pomerium/api/v1/login) and takes a pomerium_redirect_uri as an argument.
  2. The script or application opens a browser or redirects the user to the returned login page.
  3. The user completes the identity providers login flow.
  4. The identity provider makes a callback to pomerium's authenticate service (e.g. authenticate.corp.domain.example) .
  5. Pomerium's authenticate service creates a user session and redirect token, then redirects back to the managed endpoint (e.g. verify.corp.domain.example)
  6. Pomerium's proxy service makes a callback request to the original pomerium_redirect_uri with the user session and as an argument.
  7. The script or application is responsible for handling that http callback request, and securely handling the callback session (pomerium_jwt) queryparam.
  8. The script or application can now make any requests as normal to the upstream application by setting the Authorization: Pomerium ${pomerium_jwt} header.

TIP

Pomerium supports Authorization: Bearer Pomerium-${pomerium_jwt} in addition to Authorization: Pomerium ${pomerium_jwt} format.

# Example Code

Please consider see the following minimal but complete python example.

python3 scripts/programmatic_access.py \
	--dst https://verify.example.com/headers

from __future__ import absolute_import, division, print_function

import argparse
import http.server
import json
import sys
import urllib.parse
import webbrowser
from urllib.parse import urlparse
import requests

done = False

parser = argparse.ArgumentParser()
parser.add_argument("--login", action="store_true")
parser.add_argument(
    "--dst", default="https://verify.example.com/json",
)
parser.add_argument("--server", default="localhost", type=str)
parser.add_argument("--port", default=8000, type=int)
parser.add_argument(
    "--cred", default="pomerium-cred.json",
)
args = parser.parse_args()


class PomeriumSession:
    def __init__(self, jwt):
        self.jwt = jwt

    def to_json(self):
        return json.dumps(self.__dict__, indent=2)

    @classmethod
    def from_json_file(cls, fn):
        with open(fn) as f:
            data = json.load(f)
            return cls(**data)


class Callback(http.server.BaseHTTPRequestHandler):
    def log_message(self, format, *args):
        # silence http server logs for now
        return

    def do_GET(self):
        global args
        global done
        self.send_response(200)
        self.end_headers()
        response = b"OK"
        if "pomerium" in self.path:
            path = urllib.parse.urlparse(self.path).query
            path_qp = urllib.parse.parse_qs(path)
            session = PomeriumSession(
                path_qp.get("pomerium_jwt")[0],
            )
            done = True
            response = session.to_json().encode()
            with open(args.cred, "w", encoding="utf-8") as f:
                f.write(session.to_json())
                print("=> pomerium json credential saved to:\n{}".format(f.name))

        self.wfile.write(response)


def main():
    global args

    dst = urllib.parse.urlparse(args.dst)
    try:
        cred = PomeriumSession.from_json_file(args.cred)
    except:
        print("=> no credential found, let's login")
        args.login = True

    # initial login to make sure we have our credential
    if args.login:
        dst = urllib.parse.urlparse(args.dst)
        query_params = {
            "pomerium_redirect_uri": "http://{}:{}".format(args.server, args.port)
        }
        enc_query_params = urllib.parse.urlencode(query_params)
        dst_login = "{}://{}{}?{}".format(
            dst.scheme, dst.hostname, "/.pomerium/api/v1/login", enc_query_params,
        )
        response = requests.get(dst_login)
        print("=> Your browser has been opened to visit:\n{}".format(response.text))
        webbrowser.open(response.text)

        with http.server.HTTPServer((args.server, args.port), Callback) as httpd:
            while not done:
                httpd.handle_request()

    cred = PomeriumSession.from_json_file(args.cred)
    response = requests.get(
        args.dst,
        headers={
            "Authorization": "Pomerium {}".format(cred.jwt),
            "Content-type": "application/json",
            "Accept": "application/json",
        },
    )
    print(
        "==> request\n{}\n==> response.status_code\n{}\n==>response.text\n{}\n".format(
            args.dst, response.status_code, response.text
        )
    )


if __name__ == "__main__":
    main()

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