seamless

seamless provides an easy way to obtain an https session token via ssh. It automates creation of user accounts and manages their authorized_keys as well as session token creation via forced ssh commands. The authentication flow is as follows:

• A client connects to seamless-realm@seamless-host via ssh and authenticates with a public key. The key is restricted to only execute the token creation command of the seamless binary. The seamless command returns session token that is signed with a secret specific to seamless-realm.

  $ ssh -T seamless-realm@seamless-host
  username.VgfAwA.v-xKIZh3qYawqcm2RRh4q-LPfVE
  

• The client sends the obtained token in the HTTP Authorization header of its requests to protected-app. The app uses the shared secret to validate the token.

  GET / HTTP/1.1
  Host: protected-app
  Authorization: seamless username.VgfAwA.v-xKIZh3qYawqcm2RRh4q-LPfVE

Installation

From a deb package:

$ wget https://github.com/emulbreh/seamless/releases/download/v0.1.0/seamless_0.1.0_amd64.deb
$ sudo dpkg -i seamless_0.1.0_amd64.deb

As Python package:

$ pip install seamless

Setting up a seamless realm

A seamless realm is a user account on seamless-host. The creation and management of authorized_keys of these accounts is handled by seamless.

$ sudo seamless init seamless-realm
$ sudo seamless add seamless-realm /path/to/public/key --user username

A user with this public key is now able to get tokens via ssh:

$ ssh -T seamless-realm@seamless-host
username.VgfOLQ.EB6NTfXiyv7dWSKUMQJ38JXa5aw

or from Python

>>> import seamless
>>> seamless.get_token('seamless-realm@seamless-host')
'username.VgfOBA.dRBDY5EUmQvhB8OnqPDWlC1tml4'

Protecting a webservice with WSGI middleware

seamless ships with WSGI middleware that verifies that a valid seamless token is passed via the Authorization header.

from seamless.wsgi import SeamlessMiddleware

app = ...

app = SeamlessMiddleware(app, max_age=60, secret='...')

Requests without a valid Authorization header will be rejected with a 401 response.

Making requests to such a protected app is made easy with an auth plugin for requests:

import requests
from seamless.requests import SeamlessAuth

session = requests.Session()
session.auth = SeamlessAuth('name@seamless-host')

session.get('http://protected-app/')

The token obtained from seamless-host is cached. It will be be automatically refreshed when it expires, and the failing request retried.

Caveats

• If token validation is performed on a different host than token creation, clock skew may result in tokens that expire too early or too late.