About

acme-proxy allows users to get certificates from any certificate authority that supports ACME protocol (such as LetsEncrypt, Sectigo, Digicert etc.) without opening http/80 to the internet or distributing api keys for your DNS server! This is a standalone ACME server built on step-ca that operates in registration authority (RA) mode. It accepts certificate orders and validates certificate requests using the ACME protocol (RFC 8555), but does NOT sign certificates or store private keys.

Documentation

Checkout our documentation site for detailed examples on user guide, installation instructions, configuration etc.

Use Cases

This architecture addresses typical enterprise constraints that prevent direct certificate issuance from LetsEncrypt:

HTTP-01 Challenge Limitations:

Security policies prohibit exposing port 80 to the public internet.

DNS-01 Challenge Limitations:

Legacy DNS infrastructure lacks REST API support or ACME client integration
Security policies restrict distribution of API tokens or TSIG keys for large DNS zones

For more information on security considerations when using DNS-01 TXT challenge:

How acme-proxy mitigates security risks

HTTP/80 exposure is limited to a trusted internal host rather than the global internet which is the case when using LetsEncrypt.
No distributing DNS related api key or tsig key to ACME clients.

How It Works

acme-proxy runs as an ACME server inside your trusted network, acting as an intermediary between your internal infrastructure and an upstream certificate authority which signs the certificate.

Your internal server (behind a firewall perimeter) requests a certificate from acme-proxy using standard ACME client such as certbot, acme.sh or cert-manager.io if you're using Kubernetes.
acme-proxy presents cryptographic challenges to verify domain ownership.
Once validation succeeds, acme-proxy forwards the certificate signing request to an external certificate authority for signing
acme-proxy retrieves the signed certificate bundle and returns it to your server

To get signed certificates from an external CA acme-proxy supports two modes of operations:

1. External Account Binding (EAB)

Some commercial certificate authorities allow their customers to validate their apex domain (example.com) once and issue an EAB key. Using this key customers can get certs for *.example.com without having to validate every domain or subdomain (say foo.example.com) individually.

Note: LetsEncrypt does not support EAB. However, commercial CAs such as Sectigo, ZeroSSL, DigiCert do.

2. DNS01-TXT

Lego is a well known ACME client which supports over 200 DNS providers to solve DNS01-TXT challenge. Using one of the Lego providers, acme-proxy authenticates with your DNS server and temporarily places a TXT record which the external CA can verify before issuing a signed certificate. The key benefit of using this mode is that your DNS server's API key or TSIG key lives only on acme-proxy and thus circumvents the need for distributing those credentials to all your servers.

Quick Start

curl -fsSL https://raw.githubusercontent.com/esnet/acme-proxy/main/install.sh | sudo sh
Installing binary to /opt/acme-proxy...
Creating acme-proxy service user...
Setting ownership of installation directory...
Installing systemd service...
Reloading systemd daemon...
Enabling acme-proxy service...
Created symlink /etc/systemd/system/multi-user.target.wants/acme-proxy.service → /etc/systemd/system/acme-proxy.service.
Installation complete!
Next steps:
1. Edit /opt/acme-proxy/ca.json and configure:
- dnsNames: Your ACME proxy hostname
- ca_url: Your upstream ACME CA URL
- account_email: Your account email
- eab_kid: External Account Binding Key ID
- eab_hmac_key: External Account Binding HMAC key
2. Start the service:
sudo systemctl start acme-proxy
3. Check status:
sudo systemctl status acme-proxy
sudo journalctl -u acme-proxy -f

The script installs acme-proxy as a systemd service with sensible defaults, all of which can be overridden with environment variables:

# Default values (all overridable)
INSTALL_DIR="${INSTALL_DIR:-/opt/acme-proxy}"
DB_DIR="${DB_DIR:-${INSTALL_DIR}/db}"
CONFIG_FILE="${CONFIG_FILE:-${INSTALL_DIR}/ca.json}"
SERVICE_USER="${SERVICE_USER:-acme-proxy}"
SERVICE_GROUP="${SERVICE_GROUP:-acme-proxy}"

Configure

Review and update configuration options in ca.json before starting the acme-proxy server.

vim ca.json

Refer to the documentation for full set of configuration options. For a quick start the most relevant config bits are:

{
"dnsNames": ["acme-proxy.example.com"],
..."authority": {
"type": "externalcas",
"config": {
"ca_url": "",
"account_email": "",
"eab_kid": "",
"eab_hmac_key": "",
"dns01_txt":{
"providers": "",
"dns_servers":"",
"env_vars": {}
}
}
},
..."commonName": "acme-proxy.example.com"
}

Most commercial certificate authorities (such as Sectigo) support certificate issuance over external account binding. You will need to get EAB credentials i.e HMAC Key and Key ID associated with your account. To get signed certs from CertiNext/InCommon use https://acme-us.certinext.io/v1/directory as shown below

"ca_url": "https://acme-us.certinext.io/v1/directory""account_email": "certadmin@example.com",
"eab_kid": "",
"eab_hmac_key": "",

To get certificates signed from LetsEncrypt use the following config options

"ca_url": "https://acme-v02.api.letsencrypt.org/directory""account_email": "certadmin@example.com",
"dns01_txt": {
"provider": "lego-dns-provider-code",
"dns_servers": ["8.8.8,8", "1.1.1.1", "2606:4700:4700::1111"],
"env_vars": {
"LEGO_PROVIDER_API_KEY": "xxxxxxx",
}
}

Field	Description
`dns01_txt.provider`	Lego Provider CLI Flag name
`dns01_txt.dns_servers`	Use your authoritative DNS server's addresses to avoid caching/TTL problems
`dns01_txt.env_vars`	Environment variables specific to your Lego DNS Provider for authentication

Starting acme-proxy

After configuring ca.json file simply start the systemd service

sudo systemctl start acme-proxy

Upon starting acme-proxy it automatically obtains a SSL certificate for itself as part of bootstrapping. This certificate and it's private key are stored in memory and are automatically rotated using the EAB credentials provided in ca.json

$ sudo systemctl status acme-proxy
badger 2025/07/15 22:12:24 INFO: All 1 tables opened in 0s
badger 2025/07/15 22:12:24 INFO: Replaying file id: 0 at offset: 105133
badger 2025/07/15 22:12:24 INFO: Replay took: 5.99µs
2025/07/15 22:12:25 Building new tls configuration using step-ca x509 Signer Interface
2025/07/15 22:12:25 Initializing ACME client...
2025/07/15 22:12:25 [INFO] acme: Registering account for admin@example.com
2025/07/15 22:12:26 ACME client initialized successfully
2025/07/15 22:12:26 Processing certificate request for domains: [proxy.example.com]
2025/07/15 22:12:26 Starting certificate request processing for domains: [proxy.example.com]
2025/07/15 22:12:26 [INFO] [proxy.example.com] acme: Obtaining bundled SAN certificate given a CSR
2025/07/15 22:12:27 [INFO] [proxy.example.com] AuthURL: https://acme.sectigo.com/v2/InCommonRSAOV/authz/sx4qvINAdWw2IjplmyH6kg
2025/07/15 22:12:27 [INFO] [proxy.example.com] acme: authorization already valid; skipping challenge
2025/07/15 22:12:27 [INFO] [proxy.example.com] acme: Validations succeeded; requesting certificates
2025/07/15 22:12:27 [INFO] Wait for certificate [timeout: 30s, interval: 500ms]
2025/07/15 22:12:33 [INFO] [proxy.example.com] Server responded with a certificate.
2025/07/15 22:12:33 Successfully obtained certificate from InCommon for domains: [proxy.example.com]
2025/07/15 22:12:33 Starting Smallstep CA/0000000-dev (linux/amd64)
2025/07/15 22:12:33 Documentation: https://u.step.sm/docs/ca
2025/07/15 22:12:33 Community Discord: https://u.step.sm/discord
2025/07/15 22:12:33 Config file: ca.json
2025/07/15 22:12:33 The primary server URL is https://acmeproxy.example.com:443
2025/07/15 22:12:33 Root certificates are available at https://acmeproxy.example.com:443/roots.pem
2025/07/15 22:12:33 X.509 Root Fingerprint: a6cf64dbb4c8d5fd19ce48896068db03b533a8d1336c6256a87d00cbb3def3ea
2025/07/15 22:12:33 Serving HTTPS on proxy.example.com:443 ...

Obtaining a certificate

While the example below uses acme.sh as the ACME client in standalone mode, we've also tested using certbot and cert-manager on Kubernetes with equal success. For more examples see user guide.

$ ./acme.sh --issue \
--server https://acmeproxy.example.com/acme/acme/directory \
--domain myserver.example.com \
--standalone \
--listen-v6
[Tue 15 Jul 22:41:01 CDT 2025] Using CA: https://acmeproxy.example.com/acme/acme/directory
[Tue 15 Jul 22:41:01 CDT 2025] Standalone mode.
[Tue 15 Jul 22:41:01 CDT 2025] Creating domain key
[Tue 15 Jul 22:41:01 CDT 2025] The domain key is here: /root/.acme.sh/myserver.example.com_ecc/myserver.example.com.key
[Tue 15 Jul 22:41:01 CDT 2025] Single domain='myserver.example.com'
[Tue 15 Jul 22:41:02 CDT 2025] Getting webroot for domain='myserver.example.com'
[Tue 15 Jul 22:41:02 CDT 2025] Verifying: myserver.example.com
[Tue 15 Jul 22:41:02 CDT 2025] Standalone mode server
[Tue 15 Jul 22:41:04 CDT 2025] Success
[Tue 15 Jul 22:41:04 CDT 2025] Verification finished, beginning signing.
[Tue 15 Jul 22:41:04 CDT 2025] Let's finalize the order.[Tue 15 Jul 22:41:04 CDT 2025] Le_OrderFinalize='https://acmeproxy.example.com/acme/acme/order/ugickkyMzE0hoHZhBLGuGqG3ab1N0hwz/finalize'[Tue 15 Jul 22:41:12 CDT 2025] Downloading cert.[Tue 15 Jul 22:41:12 CDT 2025] Le_LinkCert='https://acmeproxy.example.com/acme/acme/certificate/b3A7d7rZA78ijaKwcR0n5xtxf8PAeE1v'[Tue 15 Jul 22:41:13 CDT 2025] Cert success.-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----[Tue 15 Jul 22:41:13 CDT 2025] Your cert is in: /root/.acme.sh/myserver.example.com_ecc/myserver.example.com.cer[Tue 15 Jul 22:41:13 CDT 2025] Your cert key is in: /root/.acme.sh/myserver.example.com_ecc/myserver.example.com.key[Tue 15 Jul 22:41:13 CDT 2025] The intermediate CA cert is in: /root/.acme.sh/myserver.example.com_ecc/ca.cer[Tue 15 Jul 22:41:13 CDT 2025] And the full-chain cert is in: /root/.acme.sh/myserver.example.com_ecc/fullchain.cer

Verify

Let's decode the certificate just to be sure ;-)

$ openssl x509 -in myserver.example.com.cer -noout -text
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
13:1c:e0:69:50:13:f6:04:68:f2:a7:9f:48:d5:4c:87
Signature Algorithm: ecdsa-with-SHA256
Issuer: C = US, O = Internet2, CN = InCommon ECC Server CA 2
Validity
Not Before: Jul 16 00:00:00 2025 GMT
Not After : Jul 16 23:59:59 2026 GMT
Subject: C = US, ST = California, O = Energy Sciences Network, CN = myserver.example.com
Subject Public Key Info:

We have our certificate signed by our certificate authority i.e InCommon 🎉

Benefits

Using ACME with commercial CAs in enterprise environments provides several advantages:

Trusted Certificates:

Certificates are signed by publicly trusted CAs are already in system trust stores
Eliminates the operational burden of distributing and maintaining custom root certificates across endpoints, servers, and client devices

Automation and Self-Service:

Leverage standard ACME clients (Certbot, acme.sh, cert-manager.io) for certificate issuance, automatic renewals.
Enable self-service certificate requests for development and infrastructure teams

Contribute

Please read our contribution guidelines before submitting with a pull request.

Name		Name	Last commit message	Last commit date
.github		.github
ansible		ansible
develop		develop
docs		docs
externalcas		externalcas
.gitignore		.gitignore
.gitmodules		.gitmodules
.pre-commit-config.yaml		.pre-commit-config.yaml
CONTRIBUTING.md		CONTRIBUTING.md
Dockerfile		Dockerfile
LICENSE		LICENSE
Makefile		Makefile
README.md		README.md
ca.json		ca.json
go.mod		go.mod
go.sum		go.sum
install.sh		install.sh
main.go		main.go

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