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Join the chat at https://gitter.im/Daplie/letsencrypt-express

| letsencrypt (library) | letsencrypt-cli | letsencrypt-express | letsencrypt-koa | letsencrypt-hapi |


Automatic Let's Encrypt HTTPS Certificates for node.js

See Also


These aren't the droids you're looking for.

This is a low-level library for implementing CLIs, system tools, and abstracting storage backends (file vs db, etc). This is not the thing to use in your webserver directly.

Use letsencrypt-express if...

you are planning to use one of these:

Use letsencrypt-cli if...

You are planning to use one of these:

  • bash
  • fish
  • zsh
  • cmd.exe
  • PowerShell


npm install --save letsencrypt



There are NO DEFAULTS.

A number of constants (such as LE.stagingServerUrl and LE.configDir) are exported for your convenience, but all required options must be specified by the library invoking the call.

Open an issue if you need a variable for something that isn't there yet.

var LE = require('letsencrypt');

var config = {
  server: LE.stagingServerUrl                               // or LE.productionServerUrl

, configDir: require('homedir')() + '/letsencrypt/etc'      // or /etc/letsencrypt or wherever

, privkeyPath: ':config/live/:hostname/privkey.pem'         //
, fullchainPath: ':config/live/:hostname/fullchain.pem'     // Note: both that :config and :hostname
, certPath: ':config/live/:hostname/cert.pem'               //       will be templated as expected
, chainPath: ':config/live/:hostname/chain.pem'             //

, debug: false

var handlers = {
  setChallenge: function (opts, hostname, key, val, cb) {}  // called during the ACME server handshake, before validation
, removeChallenge: function (opts, hostname, key, cb) {}    // called after validation on both success and failure
, getChallenge: function (opts, hostname, key, cb) {}       // this is special because it is called by the webserver
                                                            // (see letsencrypt-cli/bin & letsencrypt-express/standalone),
                                                            // not by the library itself

, agreeToTerms: function (tosUrl, cb) {}                    // gives you an async way to expose the legal agreement
                                                            // (terms of use) to your users before accepting

var le = LE.create(config, handlers);

                                                              // checks :conf/renewal/:hostname.conf
le.register({                                                 // and either renews or registers

  domains: ['example.com']                                    // CHANGE TO YOUR DOMAIN
, email: 'user@email.com'                                     // CHANGE TO YOUR EMAIL
, agreeTos: false                                             // set to true to automatically accept an agreement
                                                              // which you have pre-approved (not recommended)
}, function (err) {

  if (err) {
    // Note: you must have a webserver running
    // and expose handlers.getChallenge to it
    // in order to pass validation
    // See letsencrypt-cli and or letsencrypt-express
    console.error('[Error]: node-letsencrypt/examples/standalone');
  } else {

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.


LetsEncrypt.create(leConfig, handlers, backend)           // wraps a given "backend" (the python or node client)
LetsEncrypt.stagingServer                                 // string of staging server for testing

le.middleware()                                           // middleware for serving webrootPath to /.well-known/acme-challenge
le.sniCallback(hostname, function (err, tlsContext) {})   // uses fetch (below) and formats for https.SNICallback
le.register({ domains, email, agreeTos, ... }, cb)        // registers or renews certs for a domain
le.fetch({domains, email, agreeTos, ... }, cb)            // fetches certs from in-memory cache, occasionally refreshes from disk
le.registrationFailureCallback(err, args, certInfo, cb)   // called when registration fails (not implemented yet)

LetsEncrypt.create(backend, leConfig, handlers)


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.


{ 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 registration as webrootPath (which overwrites leConfig.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.


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


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.


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


  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

  { cert: "contents of fullchain.pem"
  , key: "contents of privkey.pem"
  , renewedAt: <date in milliseconds>
  , duration: <duration in milliseconds (90-days)>


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

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

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

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)

Change History

  • v1.5.0 now using letiny-core v2.0.0 and rsa-compat
  • v1.4.x I can't remember... but it's better!
  • v1.1.0 Added letiny-core, removed node-letsencrypt-python
  • v1.0.2 Works with node-letsencrypt-python
  • v1.0.0 Thar be dragons


Dual-licensed MIT and Apache-2.0