letsencrypt

Let's Encrypt for node.js

• Automatic HTTPS with Express
• Automatic renewal (in-process)
• safe for use with node cluster
• configurable for automatic registration (in-process)
• usable via commandline as well

Install

npm install --save letsencrypt

Right now this uses letsencrypt-python, but it's built to be able to use a pure javasript version.

# install the python client (takes 2 minutes normally, 20 on a rasberry pi)
git clone https://github.com/letsencrypt/letsencrypt
pushd letsencrypt

./letsencrypt-auto

Usage Examples

Here's a small snippet:

le.register({
  domains: ['example.com', 'www.example.com']
, email: 'user@example.com'
, agreeTos: true
, webrootPath: '/srv/www/example.com/public'
}, function (err, certs) {
  // do stuff
});

However, due to the nature of what this library does, it has a few more "moving parts" than what makes sense to show in a minimal snippet.

• commandline (standalone with "webroot")

# manual standalone registration via commandline
# (runs against testing server on tls port 5001)
node examples/commandline.js example.com,www.example.com user@example.net agree

# automatic registration and renewal (certs install as you visit the site for the first time)
# (runs against testing server on tls port 5001)
node examples/commandline.js example.com,www.example.com user@example.net agree

• expressjs (fully automatic https)

non-root

If you want to run this as non-root, you can.

You just have to set node to be allowed to use root ports

# node
sudo setcap cap_net_bind_service=+ep /usr/local/bin/node

and then make sure to set all of of the following to a directory that your user is permitted to write to

• webrootPath
• configDir
• workDir (python backend only)
• logsDir (python backend only)

See Also

• See Examples
• Let's Encrypt in (exactly) 90 seconds with Caddy
• lego: Let's Encrypt for golang

API

• LetsEncrypt.create(backend, bkDefaults, handlers)
• le.middleware()
• le.sniCallback(hostname, function (err, tlsContext) {})
• le.register({ domains, email, agreeTos, ... }, cb)
• le.fetch({domains, email, agreeTos, ... }, cb)
• le.validate(domains, cb)
• le.registrationFailureCallback(err, args, certInfo, cb)

LetsEncrypt.create(backend, bkDefaults, handlers)

backend

Currently only letsencrypt-python is supported, but we plan to work on native javascript support in February or so (when ECDSA keys are available).

If you'd like to help with that, see how to write a backend below and also look at the wrapper backend-python.js.

Example:

{ fetch: function (args, cb) {
    // cb(err) when there is an actual error (db, fs, etc)
    // cb(null, null) when the certificate was NOT available on disk
    // cb(null, { cert: '<fullchain.pem>', key: '<privkey.pem>', renewedAt: 0, duration: 0 }) cert + meta
  }
, register: function (args, setChallenge, cb) {
    // setChallenge(hostnames, key, value, cb) when a challenge needs to be set
    // cb(err) when there is an error
    // cb(null, null) when the registration is successful, but fetch still needs to be called
    // cb(null, cert /*see above*/) if registration can easily return the same as fetch
  }
}

bkDefualts

The arguments passed here (typically webpathRoot, configDir, etc) will be merged with any args (typically domains, email, and agreeTos) and passed to the backend whenever it is called.

Typically the backend wrapper will already merge any necessary backend-specific arguments.

Example:

{ webrootPath: __dirname, '/acme-challenge'
, fullchainTpl: '/live/:hostname/fullchain.pem'
, privkeyTpl: '/live/:hostname/fullchain.pem'
, configDir: '/etc/letsencrypt'
}

Note: webrootPath can be set as a default, semi-locally with webrootPathTpl, or per regesitration as webrootPath (which overwrites defaults.webrootPath).

handlers optional

h.setChallenge(hostnames, name, value, cb):

default is to write to fs

h.getChallenge(hostnames, value cb)

default is to read from fs

h.sniRegisterCallback(args, currentCerts, cb)

The default is to immediately call cb(null, null) and register (or renew) in the background during the SNICallback phase. Right now it isn't reasonable to renew during SNICallback, but around February when it is possible to use ECDSA keys (as opposed to RSA at present), registration will take very little time.

This will not be called while another registration is already in progress.

SECURITY WARNING: If you use this option with a custom h.validate(), make sure that args.domains refers to domains you expect, otherwise an attacker will spoof SNI and cause your server to rate-limit letsencrypt.org and get blocked. Note that le.validate() will check A records before attempting to register to help prevent such possible attacks.

h.validate(domains, cb)

When specified this will override le.validate(). You will need to do this if the ip address of this server is not one specified in the A records for your domain.

le.middleware()

An express handler for /.well-known/acme-challenge/<challenge>. Will call getChallenge([hostname], key, cb) if present or otherwise read challenge from disk.

Example:

app.use('/', le.middleware())

le.sniCallback(hostname, function (err, tlsContext) {});

Will call fetch. If fetch does not return certificates or returns expired certificates it will call sniRegisterCallback(args, currentCerts, cb) and then return the error, the new certificates, or call fetch a final time.

Example:

var server = require('https').createServer({ SNICallback: le.sniCallback, cert: '...', key: '...' });
server.on('request', app);

le.register({ domains, email, agreeTos, ... }, cb)

Get certificates for a domain

Example:

le.register({
  domains: ['example.com', 'www.example.com']
, email: 'user@example.com'
, webrootPath: '/srv/www/example.com/public'
, agreeTos: true
}, function (err, certs) {
  // err is some error

  console.log(certs);
  /*
  { cert: "contents of fullchain.pem"
  , key: "contents of privkey.pem"
  , renewedAt: <date in milliseconds>
  , duration: <duration in milliseconds (90-days)>
  }
  */
});

le.isValidDomain(hostname)

returns true if hostname is a valid ascii or punycode domain name.

(also exposed on the main exported module as LetsEncrypt.isValidDomain())

le.validate(args, cb)

Used internally, but exposed for convenience. Checks LetsEncrypt.isValidDomain() and then checks to see that the current server

Called before backend.register() to validate the following:

• the hostnames don't use any illegal characters
• the server's actual public ip (via api.apiify.org)
• the A records for said hostnames

le.fetch(args, cb)

Used internally, but exposed for convenience.

Checks in-memory cache of certificates for args.domains and calls then calls backend.fetch(args, cb) after merging args if necessary.

le.registrationFailureCallback(err, args, certInfo, cb)

Not yet implemented

Backends

• letsencrypt-python (complete)
• lejs (in progress)

How to write a backend

A backend must implement (or be wrapped to implement) this API:

• fetch(hostname, cb) will cb(err, certs) with certs from disk (or null or error)
• register(args, challengeCb, done) will register and or renew a cert
  • args = { domains, email, agreeTos } MUST check that agreeTos === true
  • challengeCb = function (challenge, cb) { } handle challenge as needed, call cb()

This is what args looks like:

{ domains: ['example.com', 'www.example.com']
, email: 'user@email.com'
, agreeTos: true
, configDir: '/etc/letsencrypt'
, fullchainTpl: '/live/:hostname/fullchain.pem'  // :hostname will be replaced with the domainname
, privkeyTpl: '/live/:hostname/privkey.pem'
, webrootPathTpl: '/srv/www/:hostname/public'
, webrootPath: '/srv/www/example.com/public'    // templated from webrootPathTpl
}

This is what the implementation should look like:

(it's expected that the client will follow the same conventions as the python client, but it's not necessary)

return {
  fetch: function (args, cb) {
    // NOTE: should return an error if args.domains cannot be satisfied with a single cert
    // (usually example.com and www.example.com will be handled on the same cert, for example)
    if (errorHappens) {
      // return an error if there is an actual error (db, etc)
      cb(err);
      return;
    }
    // return null if there is no error, nor a certificate
    else if (!cert) {
      cb(null, null);
      return;
    }

    // NOTE: if the certificate is available but expired it should be
    // returned and the calling application will decide to renew when
    // it is convenient

    // NOTE: the application should handle caching, not the library

    // return the cert with metadata
    cb(null, {
      cert: "/*contcatonated certs in pem format: cert + intermediate*/"
    , key: "/*private keypair in pem format*/"
    , renewedAt: new Date()       // fs.stat cert.pem should also work
    , duration: 90 * 24 * 60 * 60 * 1000  // assumes 90-days unless specified
    });
  }
, register: function (args, challengeCallback, completeCallback) {
    // **MUST** reject if args.agreeTos is not true

    // once you're ready for the caller to know the challenge
    if (challengeCallback) {
      challengeCallback(challenge, function () {
        continueRegistration();
      })
    } else {
      continueRegistration();
    }

    function continueRegistration() {
      // it is not necessary to to return the certificates here
      // the client will call fetch() when it needs them
      completeCallback(err);
    }
  }
};

LICENSE

Dual-licensed MIT and Apache-2.0

See LICENSE