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acme: Automatic Let's Encrypt certificate serving and Lua implementation of ACMEv2 procotol

Installation

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CentOS/RHEL 7 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua-resty-acme

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua5.1-resty-acme

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-acme v0.12.0 released on Sep 05 2023.

Automatic Let's Encrypt certificate serving (RSA + ECC) and pure Lua implementation of the ACMEv2 protocol.

http-01 and tls-alpn-01 challenges are supported.

Build Status luarocks opm

简体中文

Description

This library consists of two parts:

  • resty.acme.autossl: automatic lifecycle management of Let's Encrypt certificates
  • resty.acme.client: Lua implementation of ACME v2 protocol

Install using opm:

opm install fffonion/lua-resty-acme

Alternatively, to install using luarocks:

luarocks install lua-resty-acme
## manually install a luafilesystem
luarocks install luafilesystem

Note you will need to manually install luafilesystem when using LuaRocks. This is made to maintain backward compatibility.

This library uses an FFI-based openssl backend, which currently supports OpenSSL 1.1.1, 1.1.0 and 1.0.2 series.

Status

Production.

Synopsis

Create account private key and fallback certs:

## create account key
openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:4096 -out /etc/openresty/account.key
## create fallback cert and key
openssl req -newkey rsa:2048 -nodes -keyout /etc/openresty/default.key -x509 -days 365 -out /etc/openresty/default.pem

Use the following example config:

events {}

http {
    resolver 8.8.8.8 ipv6=off;

    lua_shared_dict acme 16m;

    # required to verify Let's Encrypt API
    lua_ssl_trusted_certificate /etc/ssl/certs/ca-certificates.crt;
    lua_ssl_verify_depth 2;

    init_by_lua_block {
        require("resty.acme.autossl").init({
            -- setting the following to true
            -- implies that you read and accepted https://letsencrypt.org/repository/
            tos_accepted = true,
            -- uncomment following for first time setup
            -- staging = true,
            -- uncomment following to enable RSA + ECC double cert
            -- domain_key_types = { 'rsa', 'ecc' },
            -- uncomment following to enable tls-alpn-01 challenge
            -- enabled_challenge_handlers = { 'http-01', 'tls-alpn-01' },
            account_key_path = "/etc/openresty/account.key",
            account_email = "youemail@youdomain.com",
            domain_whitelist = { "example.com" },
        })
    }

    init_worker_by_lua_block {
        require("resty.acme.autossl").init_worker()
    }

    server {
        listen 80;
        listen 443 ssl;
        server_name example.com;

        # fallback certs, make sure to create them before hand
        ssl_certificate /etc/openresty/default.pem;
        ssl_certificate_key /etc/openresty/default.key;

        ssl_certificate_by_lua_block {
            require("resty.acme.autossl").ssl_certificate()
        }

        location /.well-known {
            content_by_lua_block {
                require("resty.acme.autossl").serve_http_challenge()
            }
        }
    }
}

When testing deployment, it's recommanded to uncomment the staging = true to allow an end-to-end test of your environment. This can avoid configuration failure result into too many requests that hits rate limiting on Let's Encrypt API.

By default autossl only creates RSA certificates. To use ECC certificates or both, uncomment domain_key_types = { 'rsa', 'ecc' }. Note that multiple certificate chain is only supported by NGINX 1.11.0 or later.

A certificate will be queued to create after Nginx seen request with such SNI, which might take tens of seconds to finish. During the meantime, requests with such SNI are responsed with the fallback certificate.

Note that domain_whitelist or domain_whitelist_callback must be set to include your domain that you wish to server autossl, to prevent potential abuse using fake SNI in SSL handshake. domain_whitelist defines a table that includes all domains should be included, and domain_whitelist_callback defines a function that accepts domain as parameter and return boolean to indicate if it should be included. 

domain_whitelist = { "domain1.com", "domain2.com", "domain3.com" },

To match a pattern in your domain name, for example all subdomains under example.com, use:

domain_whitelist_callback = function(domain, is_new_cert_needed)
    return ngx.re.match(domain, [[\.example\.com$]], "jo")
end

Furthermore, since checking domain whitelist is running in certificate phase. It's possible to use cosocket API here. Do note that this will increase the SSL handshake latency.

domain_whitelist_callback = function(domain, is_new_cert_needed)
    -- send HTTP request
    local http = require("resty.http")
    local res, err = httpc:request_uri("http://example.com")
    -- access the storage
    local acme = require("resty.acme.autossl")
    local value, err = acme.storage:get("key")
    -- get cert from resty LRU cache
    -- cached = { pkey, cert } or nil if cert is not in cache
    local cached, staled, flags = acme.get_cert_from_cache(domain, "rsa")
    -- do something to check the domain
    -- return is_domain_included
end}),

domain_whitelist_callback function is provided with a second argument, which indicates whether the certificate is about to be served on incoming HTTP request (false) or new certificate is about to be requested (true). This allows to use cached values on hot path (serving requests) while fetching fresh data from storage for new certificates. One may also implement different logic, e.g. do extra checks before requesting new cert.

In case of certificate request failure one may want to prevent ACME client to request another certificate immediatelly. By default, the cooloff period it is set to 300 seconds (5 minutes). It may be customized with failure_cooloff or with failure_cooloff_callback function, e.g. to implement exponential backoff.

    failure_cooloff_callback = function(domain, count)
      if count == 1 then
        return 600 -- 10 minutes
      elseif count == 2 then
        return 1800 -- 30 minutes
      elseif count == 3 then
        return 3600 -- 1 hour
      elseif count == 4 then
        return 43200 -- 12 hours
      elseif count == 5 then
        return 43200 -- 12 hours
      else
        return 86400 -- 24 hours
      end
    end

tls-alpn-01 challenge

tls-alpn-01 challenge is currently supported on Openresty 1.15.8.x, 1.17.8.x and 1.19.3.x.

Click to expand sample config 
events {}

http {
    resolver 8.8.8.8 ipv6=off;

    lua_shared_dict acme 16m;

    # required to verify Let's Encrypt API
    lua_ssl_trusted_certificate /etc/ssl/certs/ca-certificates.crt;
    lua_ssl_verify_depth 2;

    init_by_lua_block {
        require("resty.acme.autossl").init({
            -- setting the following to true
            -- implies that you read and accepted https://letsencrypt.org/repository/
            tos_accepted = true,
            -- uncomment following for first time setup
            -- staging = true,
            -- uncomment folloing to enable RSA + ECC double cert
            -- domain_key_types = { 'rsa', 'ecc' },
            -- uncomment following to enable tls-alpn-01 challenge
            enabled_challenge_handlers = { 'http-01', 'tls-alpn-01' },
            account_key_path = "/etc/openresty/account.key",
            account_email = "youemail@youdomain.com",
            domain_whitelist = { "example.com" },
            storage_adapter = "file",
        })
    }
    init_worker_by_lua_block {
        require("resty.acme.autossl").init_worker()
    }

    server {
        listen 80;
        listen unix:/tmp/nginx-default.sock ssl;
        # listen unix:/tmp/nginx-default.sock ssl proxy_protocol;
        server_name example.com;

        # set_real_ip_from unix:;
        # real_ip_header proxy_protocol;

        # fallback certs, make sure to create them before hand
        ssl_certificate /etc/openresty/default.pem;
        ssl_certificate_key /etc/openresty/default.key;

        ssl_certificate_by_lua_block {
            require("resty.acme.autossl").ssl_certificate()
        }

        location /.well-known {
            content_by_lua_block {
                require("resty.acme.autossl").serve_http_challenge()
            }
        }
    }
}

stream {
    init_worker_by_lua_block {
        require("resty.acme.autossl").init({
            -- setting the following to true
            -- implies that you read and accepted https://letsencrypt.org/repository/
            tos_accepted = true,
            -- uncomment following for first time setup
            -- staging = true,
            -- uncomment folloing to enable RSA + ECC double cert
            -- domain_key_types = { 'rsa', 'ecc' },
            -- uncomment following to enable tls-alpn-01 challenge
            enabled_challenge_handlers = { 'http-01', 'tls-alpn-01' },
            account_key_path = "/etc/openresty/account.key",
            account_email = "youemail@youdomain.com",
            domain_whitelist = { "example.com" },
            storage_adapter = "file"
        })
        require("resty.acme.autossl").init_worker()
    }

    map $ssl_preread_alpn_protocols $backend {
        ~\bacme-tls/1\b unix:/tmp/nginx-tls-alpn.sock;
        default unix:/tmp/nginx-default.sock;
    }

    server {
            listen 443;
            listen [::]:443;

            ssl_preread on;
            proxy_pass $backend;

            # proxy_protocol on;
    }

    server {
            listen unix:/tmp/nginx-tls-alpn.sock ssl;
            # listen nix:/tmp/nginx-tls-alpn.sock ssl proxy_protocol;
            ssl_certificate certs/default.pem;
            ssl_certificate_key certs/default.key;

            # requires --with-stream_realip_module
            # set_real_ip_from unix:;

            ssl_certificate_by_lua_block {
                    require("resty.acme.autossl").serve_tls_alpn_challenge()
            }

            content_by_lua_block {
                    ngx.exit(0)
            }
    }
}

In the above sample config, we set a http server and two stream server.

The very front stream server listens for 443 port and route to different upstream based on client ALPN. The tls-alpn-01 responder listens on unix:/tmp/nginx-tls-alpn.sock. All normal https traffic listens on unix:/tmp/nginx-default.sock.

                                                [stream server unix:/tmp/nginx-tls-alpn.sock ssl]
                                            Y /
[stream server 443] --- ALPN is acme-tls ?
                                            N \
                                                [http server unix:/tmp/nginx-default.sock ssl]
  • The config passed to require("resty.acme.autossl").init in both subsystem should be kept same as possible.
  • tls-alpn-01 challenge handler doesn't need any third party dependency.
  • You can enable http-01 and tls-alpn-01 challenge handlers at the same time.
  • http and stream subsystem doesn't share shm, thus considering use a storage other than shm. If you must use shm, you will need to apply this patch.

resty.acme.autossl

A config table can be passed to resty.acme.autossl.init(), the default values are:

default_config = {
  -- accept term of service https://letsencrypt.org/repository/
  tos_accepted = false,
  -- if using the let's encrypt staging API
  staging = false,
  -- the path to account private key in PEM format
  account_key_path = nil,
  -- the account email to register
  account_email = nil,
  -- number of certificate cache, per type
  cache_size = 100,
  domain_key_paths = {
    -- the global domain RSA private key
    rsa = nil,
    -- the global domain ECC private key
    ecc = nil,
  },
  -- the private key algorithm to use, can be one or both of
  -- 'rsa' and 'ecc'
  domain_key_types = { 'rsa' },
  -- restrict registering new cert only with domain defined in this table
  domain_whitelist = nil,
  -- restrict registering new cert only with domain checked by this function
  domain_whitelist_callback = nil,
  -- interval to wait before retrying after failed certificate request
  failure_cooloff = 300,
  -- function that returns interval to wait before retrying after failed certificate request
  failure_cooloff_callback = nil,
  -- the threshold to renew a cert before it expires, in seconds
  renew_threshold = 7 * 86400,
  -- interval to check cert renewal, in seconds
  renew_check_interval = 6 * 3600,
  -- the store certificates
  storage_adapter = "shm",
  -- the storage config passed to storage adapter
  storage_config = {
    shm_name = 'acme',
  },
  -- the challenge types enabled
  enabled_challenge_handlers = { 'http-01' },
  -- time to wait before signaling ACME server to validate in seconds
  challenge_start_delay = 0,
  -- if true, the request to nginx waits until the cert has been generated and it is used right away
  blocking = false,
}

If account_key_path is not specified, a new account key will be created everytime Nginx reloads configuration. Note this may trigger New Account rate limiting on Let's Encrypt API.

If domain_key_paths is not specified, a new private key will be generated for each certificate (4096-bits RSA and 256-bits prime256v1 ECC). Note that generating such key will block worker and will be especially noticable on VMs where entropy is low.

Pass config table directly to ACME client as second parameter. The following example demonstrates how to use a CA provider other than Let's Encrypt and also set the preferred chain.

resty.acme.autossl.init({
    tos_accepted = true,
    account_email = "example@example.com",
  }, {
    api_uri = "https://acme.otherca.com/directory",
    preferred_chain = "OtherCA PKI Root CA",
  }
)

See also Storage Adapters below.

When using distributed storage types, it's useful to bump up challenge_start_delay to allow changes in storage to propogate around. When challenge_start_delay is set to 0, no wait will be performed before start validating challenges.

autossl.get_certkey

syntax: certkey, err = autossl.get_certkey(domain, type?)

Return the PEM-encoded certificate and private key for domain from storage. Optionally accepts a type parameter which can be "rsa" or "ecc"; if omitted, type will default to "rsa".

resty.acme.client

client.new

syntax: c, err = client.new(config)

Create a ACMEv2 client.

Default values for config are:

default_config = {
  -- the ACME v2 API endpoint to use
  api_uri = "https://acme-v02.api.letsencrypt.org/directory",
  -- the account email to register
  account_email = nil,
  -- the account key in PEM format text
  account_key = nil,
  -- the account kid (as an URL)
  account_kid = nil,
  -- external account binding key id
  eab_kid = nil,
  -- external account binding hmac key, base64url encoded
  eab_hmac_key = nil,
  -- external account registering handler
  eab_handler = nil,
  -- storage for challenge
  storage_adapter = "shm",
  -- the storage config passed to storage adapter
  storage_config = {
    shm_name = "acme"
  },
  -- the challenge types enabled, selection of `http-01` and `tls-alpn-01`
  enabled_challenge_handlers = {"http-01"},
  -- select preferred root CA issuer's Common Name if appliable
  preferred_chain = nil,
  -- callback function that allows to wait before signaling ACME server to validate
  challenge_start_callback = nil,
}

If account_kid is omitted, user must call client:new_account() to register a new account. Note that when using the same account_key, client:new_account() will return the same kid that is previosuly registered.

If CA requires External Account Binding, user can set eab_kid and eab_hmac_key to load an existing account, or set account_email and eab_handler to register a new account. eab_hmac_key must be base64 url encoded. In later case, user must call client:new_account() to register a new account. eab_handler must be an function that accepts account_email as parameter and returns eab_kid, eab_hmac_key and error if any.

eab_handler = function(account_email)
  -- do something to register an account with account_email
  -- if err then
  --  return nil, nil, err
  -- end
  return eab_kid, eab_hmac_key
end

The following CA provider's EAB handler is supported by lua-resty-acme and user doesn't need to implement their own eab_handler:

preferred_chain is used to select a chain with matching Common Name in its root CA. For example, user can use use "ISRG Root X1" to force use the new default chain in Let's Encrypt. When no value is configured or the configured name is not found in any chain, the default chain will be used.

challenge_start_callback is a callback function to allow the client to wait before signalling ACME server to start validate challenge. It's useful in a distributed setup where challenges take time to propogate. challenge_start_callback accepts challenge_type and challenge_token. The client calls this function every second until it returns true indicating challenge should start; if this challenge_start_callback is not set, no wait will be performed.

challenge_start_callback = function(challenge_type, challenge_token)
  -- do something here
  -- if we are good
  return true
end

See also Storage Adapters below.

client:init

syntax: err = client:init()

Initialize the client, requires availability of cosocket API. This function will login or register an account.

client:order_certificate

syntax: err = client:order_certificate(domain,...)

Create a certificate with one or more domains. Note that wildcard domains are not supported as it can only be verified by dns-01 challenge.

client:serve_http_challenge

syntax: client:serve_http_challenge()

Serve http-01 challenge. A common use case will be to put this as a content_by_* block for /.well-known path.

client:serve_tls_alpn_challenge

syntax: client:serve_tls_alpn_challenge()

Serve tls-alpn-01 challenge. See this section on how to use this handler.

Storage Adapters

Storage adapters are used in autossl or acme client to storage temporary or persistent data. Depending on the deployment environment, there're currently five storage adapters available to select from. To implement a custom storage adapter, please refer to this doc.

file

Filesystem based storage. Sample configuration:

storage_config = {
    dir = '/etc/openresty/storage',
}
If dir is omitted, the OS temporary directory will be used.

luafilesystem or luafilesystem-ffi is needed when using the file storage for renewal.

shm

Lua shared dict based storage. Note this storage is volatile between Nginx restarts (not reloads). Sample configuration:

storage_config = {
    shm_name = 'dict_name',
}

redis

Redis based storage. The default config is:

storage_config = {
    host = '127.0.0.1',
    port = 6379,
    database = 0,
    -- Redis authentication key
    auth = nil,
    ssl = false,
    ssl_verify = false,
    ssl_server_name = nil,
    -- namespace as a prefix of key
    namespace = "",
}

Redis >= 2.6.0 is required as this storage requires PEXPIRE.

vault

Hashicorp Vault based storage. Only KV V2 backend is supported. The default config is:

storage_config = {
    host = '127.0.0.1',
    port = 8200,
    -- secrets kv prefix path
    kv_path = "acme",
    -- timeout in ms
    timeout = 2000,
    -- use HTTPS
    https = false,
    -- turn on tls verification
    tls_verify = true
    -- SNI used in request, default to host if omitted
    tls_server_name = nil,
    -- Auth Method, default to token, can be "token" or "kubernetes"
    auth_method = "token"
    -- Vault token
    token = nil,
    -- Vault's authentication path to use
    auth_path =  "kubernetes",
    -- The role to try and assign
    auth_role = nil,
    -- The path to the JWT
    jwt_path = "/var/run/secrets/kubernetes.io/serviceaccount/token",
    -- Vault namespace
    namespace = nil,
}

Support for different auth method

  • Token: This is the default and allows to pass a literal "token" in the configuration
  • Kubernetes: Via this method, one can utilize vault's built-in auth method for kubernetes What this basically this is take the service account token and validates it has been signed by Kubernetes CA. The major benefit here, is that config files don't expose your token anymore.

The following configurations apply here: lua -- Vault's authentication path to use auth_path = "kubernetes", -- The role to try and assign auth_role = nil, -- The path to the JWT jwt_path = "/var/run/secrets/kubernetes.io/serviceaccount/token",

consul

Hashicorp Consul based storage. The default config is:

storage_config = {
    host = '127.0.0.1',
    port = 8500,
    -- kv prefix path
    kv_path = "acme",
    -- Consul ACL token
    token = nil,
    -- timeout in ms
    timeout = 2000,
}

etcd

etcd based storage. Right now only v2 protocol is supported. The default config is:

storage_config = {
    http_host = 'http://127.0.0.1:4001',
    protocol = 'v2',
    key_prefix = '',
    timeout = 60,
    ssl_verify = false,
}

Etcd storage requires lua-resty-etcd library to installed. It can be manually installed with opm install api7/lua-resty-etcd or luarocks install lua-resty-etcd.

TODO

  • autossl: ocsp staping

Testing

Setup e2e test environment by running bash t/fixtures/prepare_env.sh.

Then run cpanm install Test::Nginx::Socket and then prove -r t.

See Also

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-acme.