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Daniel Lo Nigro 8eed75b495

Explain CNAMEs in DNS records section

2018-03-22 20:37:07 -07:00

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acme-dns

A simplified DNS server with a RESTful HTTP API to provide a simple way to automate ACME DNS challenges.

Why?

Many DNS servers do not provide an API to enable automation for the ACME DNS challenges. Those which do, give the keys way too much power. Leaving the keys laying around your random boxes is too often a requirement to have a meaningful process automation.

Acme-dns provides a simple API exclusively for TXT record updates and should be used with ACME magic "_acme-challenge" - subdomain CNAME records. This way, in the unfortunate exposure of API keys, the effetcs are limited to the subdomain TXT record in question.

So basically it boils down to accessibility and security

Features

Simplified DNS server, serving your ACME DNS challenges (TXT)
Custom records (have your required A, AAAA, NS, etc. records served)
HTTP API automatically acquires and uses Let's Encrypt TLS certificate
Limit /update API endpoint access to specific CIDR mask(s), defined in the /register request
Supports SQLite & PostgreSQL as DB backends
Rolling update of two TXT records to be able to answer to challenges for certificates that have both names: yourdomain.tld and *.yourdomain.tld, as both of the challenges point to the same subdomain.
Simple deployment (it's Go after all)

Usage

A Certbot authentication hook for acme-dns is available at: https://github.com/joohoi/acme-dns-certbot.

Using acme-dns is a three-step process (provided you already have the self-hosted server set up):

Get credentials and unique subdomain (simple POST request to eg. https://auth.acme-dns.io/register)
Create a (ACME magic) CNAME record to your existing zone, pointing to the subdomain you got from the registration. (eg. _acme-challenge.domainiwantcertfor.tld. CNAME a097455b-52cc-4569-90c8-7a4b97c6eba8.auth.example.org )
Use your credentials to POST a new DNS challenge values to an acme-dns server for the CA to validate them off of.
Crontab and forget.

API

Register endpoint

The method returns a new unique subdomain and credentials needed to update your record. Fulldomain is where you can point your own _acme-challenge subdomain CNAME record to. With the credentials, you can update the TXT response in the service to match the challenge token, later referred as ___validation_token_recieved_from_the_ca___, given out by the Certificate Authority.

Optional:: You can POST JSON data to limit the /update requests to predefined source networks using CIDR notation.

POST /register

OPTIONAL Example input

{
    "allowfrom": [
        "192.168.100.1/24",
        "1.2.3.4/32",
        "2002:c0a8:2a00::0/40"
    ]
}

Status: 201 Created

{
    "allowfrom": [
        "192.168.100.1/24",
        "1.2.3.4/32",
        "2002:c0a8:2a00::0/40"
    ],
    "fulldomain": "8e5700ea-a4bf-41c7-8a77-e990661dcc6a.auth.acme-dns.io",
    "password": "htB9mR9DYgcu9bX_afHF62erXaH2TS7bg9KW3F7Z",
    "subdomain": "8e5700ea-a4bf-41c7-8a77-e990661dcc6a",
    "username": "c36f50e8-4632-44f0-83fe-e070fef28a10"
}

Update endpoint

The method allows you to update the TXT answer contents of your unique subdomain. Usually carried automatically by automated ACME client.

POST /update

Required headers

Header name	Description	Example
X-Api-User	UUIDv4 username recieved from registration	`X-Api-User: c36f50e8-4632-44f0-83fe-e070fef28a10`
X-Api-Key	Password recieved from registration	`X-Api-Key: htB9mR9DYgcu9bX_afHF62erXaH2TS7bg9KW3F7Z`

Example input

{
    "subdomain": "8e5700ea-a4bf-41c7-8a77-e990661dcc6a",
    "txt": "___validation_token_recieved_from_the_ca___"
}

Response

Status: 200 OK

{
    "txt": "___validation_token_recieved_from_the_ca___"
}

Self-hosted

You are encouraged to run your own acme-dns instance, because you are effectively authorizing the acme-dns server to act on your behalf in providing the answer to challengeing CA, making the instance able to request (and get issued) a TLS certificate for the domain that has CNAME pointing to it.

Check out how in the INSTALL section.

Installation

Install Go 1.9 or newer
Install acme-dns: go get github.com/joohoi/acme-dns/.... This will install acme-dns to ~/go/bin/acme-dns.
Edit config.cfg to suit your needs (see configuration). acme-dns will read the configuration file from /etc/acme-dns/config.cfg or ./config.cfg
Run acme-dns. Please note that acme-dns needs to open a privileged port (53, domain), so it needs to be run with elevated privileges.

Using Docker

Pull the latest acme-dns Docker image: docker pull joohoi/acme-dns
Create directories: config for the configuration file, and data for the sqlite3 database.
Copy configuration template to config/config.cfg
Modify the config.cfg to suit your needs.
Run Docker, this example expects that you have port = "80" in your config.cfg:

docker run --rm --name acmedns                 \
 -p 53:53                                      \
 -p 80:80                                      \
 -v /path/to/your/config:/etc/acme-dns:ro      \
 -v /path/to/your/data:/var/lib/acme-dns       \
 -d joohoi/acme-dns

Docker Compose

Create directories: config for the configuration file, and data for the sqlite3 database.
Copy configuration template to config/config.cfg
Copy docker-compose.yml from the project, or create your own.
Edit the config/config.cfg and docker-compose.yml to suit your needs, and run docker-compose up -d

DNS Records

Note: In this documentation:

example.com is your domain name
auth.example.com is the subdomain you want to use for acme-dns
198.51.100.1 is the public IP address of the system running acme-dns

These values should be changed based on your environment.

You will need to add some DNS records on your domain's regular DNS server:

NS record for auth.example.com pointing to ns.auth.example.com
A record for ns.auth.example.com pointing to 198.51.100.1
If using IPv6, an AAAA record pointing to the IPv6 address
Each domain you will be authenticating will need a CNAME for a _acme-challenge subdomain added. The client you use will explain how to do this.

Testing It Out

You may want to test that acme-dns is working before using it for real queries.

Confirm that DNS lookups for the acme-dns subdomain works as expected: dig auth.example.com
Call the /register API endpoint to register a test domain:

$ curl -X POST http://auth.example.com/register
{"username":"eabcdb41-d89f-4580-826f-3e62e9755ef2","password":"pbAXVjlIOE01xbut7YnAbkhMQIkcwoHO0ek2j4Q0","fulldomain":"d420c923-bbd7-4056-ab64-c3ca54c9b3cf.auth.example.com","subdomain":"d420c923-bbd7-4056-ab64-c3ca54c9b3cf","allowfrom":[]}

Call the /update API endpoint to set a test TXT record. Pass the username, password and subdomain received from the register call performed above:

$ curl -X POST \
  -H "X-Api-User: eabcdb41-d89f-4580-826f-3e62e9755ef2" \
  -H "X-Api-Key: pbAXVjlIOE01xbut7YnAbkhMQIkcwoHO0ek2j4Q0" \
  -d '{"subdomain": "d420c923-bbd7-4056-ab64-c3ca54c9b3cf", "txt": "___validation_token_recieved_from_the_ca___"}' \
  http://auth.example.com/update

Note: The txt field must be exactly 43 characters long, otherwise acme-dns will reject it

Perform a DNS lookup to the test subdomain to confirm that everything is working properly:

$ dig @ns.auth.example.com d420c923-bbd7-4056-ab64-c3ca54c9b3cf.auth.example.com

Configuration

[general]
# dns interface
listen = ":53"
# protocol, "udp", "udp4", "udp6" or "tcp", "tcp4", "tcp6"
protocol = "udp"
# domain name to serve the requests off of 
domain = "auth.example.org"
# zone name server 
nsname = "ns1.auth.example.org"
# admin email address, where @ is substituted with .
nsadmin = "admin.example.org"
# predefined records served in addition to the TXT
records = [
    # default A
    "auth.example.org. A 192.168.1.100",
    # A 
    "ns1.auth.example.org. A 192.168.1.100",
    "ns2.auth.example.org. A 192.168.1.100",
    # NS
    "auth.example.org. NS ns1.auth.example.org.",
    "auth.example.org. NS ns2.auth.example.org.",
]
# debug messages from CORS etc
debug = false

[database]
# Database engine to use, sqlite3 or postgres
engine = "sqlite3"
# Connection string, filename for sqlite3 and postgres://$username:$password@$host/$db_name for postgres
connection = "acme-dns.db"
# connection = "postgres://user:password@localhost/acmedns_db"

[api]
# domain name to listen requests for, mandatory if using tls = "letsencrypt"
api_domain = ""
# disable registration endpoint
disable_registration = false
# autocert HTTP port, eg. 80 for answering Let's Encrypt HTTP-01 challenges. Mandatory if using tls = "letsencrypt".
autocert_port = "80"
# listen ip, default "" listens on all interfaces/addresses
ip = "127.0.0.1"
# listen port, eg. 443 for default HTTPS
port = "8080"
# possible values: "letsencrypt", "cert", "none"
tls = "none"
# only used if tls = "cert"
tls_cert_privkey = "/etc/tls/example.org/privkey.pem"
tls_cert_fullchain = "/etc/tls/example.org/fullchain.pem"
# CORS AllowOrigins, wildcards can be used
corsorigins = [
    "*"
]

[logconfig]
# logging level: "error", "warning", "info" or "debug"
loglevel = "debug"
# possible values: stdout, TODO file & integrations
logtype = "stdout"
# file path for logfile TODO
# logfile = "./acme-dns.log"
# format, either "json" or "text" 
logformat = "text"
# use HTTP header to get the client ip
use_header = false
# header name to pull the ip address / list of ip addresses from
header_name = "X-Forwarded-For"

Client