free_tls_certificates 0.1.3

A simple client/tool for Let's Encrypt or any ACME server that issues SSL certificates.

This is a work in progress!

free_tls_certificates is a Python 2/3 client library for Let’s Encrypt or any ACME server that issues TLS certificates (aka SSL certificates). The purpose of this library is to make it easier to embed Let’s Encrypt within server provisioning applications without resorting to shelling out the letsencrypt command line client.

This module is based on the low-level acme client library by the Let’s Encrypt team.

Prerequisites:

• The Let’s Encrypt ACME client library and all of its dependencies.

• The idna module (https://github.com/kjd/idna).

• The cryptography module (https://github.com/pyca/cryptography) and its dependencies (on Ubuntu: sudo apt-get install build-essential libssl-dev libffi-dev python3-dev).

Usage:

The file driver.py contains a complete, working example for how to use this client library. It is also a convenient command-line tool for provisioning a certificate, which after pip-installing the package becomes available as free_tls_certificate.

From the command line:

sudo apt-get install build-essential libssl-dev libffi-dev python3-dev python3-pip
sudo pip3 install free_tls_certificates
free_tls_certificate domain-name-1.com [domain-name-2.com ...] private.key certificate.crt /path/to/website /path/to/acme/storage

See driver.py for complete documentation.

Here’s basically how it works:

Example:

import requests.exceptions
import acme.messages

from free_tls_certificates import client

domains = ["mailinabox.email", "www.mailinabox.email"]
agree_to_tos = None  # fill this in on second run per output of exception

try:
    client.issue_certificate(
        domains,
        "path/to/some/storage",
        certificate_file="certificate.crt",
        agree_to_tos_url=agree_to_tos)

except client.NeedToAgreeToTOS as e:
    print("You need to agree to the TOS. Set this on next run:")
    print("agree_to_tos = " + repr(e.url))

except client.NeedToTakeAction as e:
    for action in e.actions:
        if isinstance(action, client.NeedToInstallFile):
            print("Install a file!")
            print("Location: " + action.url)
            print("Contents: " + action.contents)

except client.WaitABit as e:
    import datetime
    print ("Try again in %s." % (e.until_when - datetime.datetime.now()))

But see the full driver file for all of the error conditions you need to handle.

Usage Notes

You may use any Python string type (str, bytes, unicode) to pass domain names. If a domain is internationalized, use Python 2 unicode and Python 3 str instances to pass the Unicode form of the domain name. If the string is already IDNA-encoded (i.e. punycode), you may use any string type.

Note that Let’s Encrypt doesn’t yet (at the time of writing) support issuing certificates for internationalized domains.

Testing

To test the library, set up a locally running Boulder server, which is the reference implementation of an ACME server.

• Install docker.

• Download the Boulder source code from https://github.com/letsencrypt/boulder.

• Change to the directory that you put Boulder in.

• Run ./test/run-docker.sh (perhaps with sudo depending on your docker setup).

Boulder runs in its test configuration by default which performs “HTTP01” domain validation by querying the docker host machine on port 5002 no matter what domain a certificate is being requested for, which is handy for creating a test server to respond to those requests. (You still have to test with a plausible public domain name, however, so something.invalid will be rejected by your Boulder server.)

Create a virtual environment for testing if you don’t already have one:

virtualenv -ppython3 env
source env/bin/activate
pip install -r requirements.txt

Add 127.0.0.1 x1.le.wtf to your /etc/hosts file. This is for our library’s client-side verification of the domain validation check, prior to submission of the challenge response to the ACME server. We use x1.le.wtf as the test domain and it should resolve to localhost.

Start our unit test:

python test.py

This checks that the local Boulder server will issue a certificate for x1.le.wtf, and it checks other aspects of the library.