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Solve ACME http-01 challenge without opening port 80 to the internet, obtain certs from an external certificate authority.

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esnet/acme-proxy

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ACME server as a Registration Authority

Step CA is a swiss army knife for PKI. It can run as a standalone ACME server in registration authority (RA) mode. This server accepts certificate orders, and authenticates certificate requests over ACME protocol (RFC 8555). It does NOT sign certificates or store any private key. Instead, once ACME challenges are verified the certificate requests are then passed to an external certificate authority (such as InCommon) to sign and catalog. This repository implements a plugin for Step CA with InCommon as the upstream CA.

How does it work?

WARNING ⚠️

This is a work in progress. Not quite ready for production but will be soon.

TODO

  • Move config bits from env vars to ca.json
  • Implement Revoke method
  • Re-assess if GetCertificateAuthority is a requirement or not
  • Write unit tests
  • Prometheus metrics
  • Write Helm chart
  • Write admin docs
  • Write user docs

Quick Start

Installer script

curl -fsSL https://raw.githubusercontent.com/esnet/acme-proxy/refs/heads/main/install.sh | sudo sh

Build from source (Optional)

Make sure you have Go >=1.25 installed.

❯ git clone https://github.com/esnet/acme-proxy.git
❯ make

Usage

Review/configure the ca.json file before starting the server

vim ca.json

The most important part of the config is this section

  "authority": {
    "type": "externalcas",
    "config": {
      "ca_url": "",
      "account_email": "",
      "eab_kid": "",
      "eab_hmac_key": "",
      "certlifetime": 30,
      "metrics": {
        "enabled": true,
        "port": 9123
      }
    },
    ...
  }

ca_url : ACME directory URL of external certificate authority. To get signed certs from InCommon use https://acme.sectigo.com/v2/InCommonRSAOV

Most commercial certificate authorities (such as Sectigo) support ACME over external account binding (EAB). You will need to to get your EAB credentials i.e HMAC Key and Key ID related to your account.

  "account_email": "[email protected]",
  "eab_kid": "",
  "eab_hmac_key": "",

Starting the ACME server

Upon starting the ACME server it automatically obtains a SSL/TLS certificate for itself.

$ ./step-ca ca.json
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 [email protected]
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, we've also tested using certbot with equal success.

$ ./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-----
MIIE1jCCBHygAwIBAgIQExzgaVAT9gRo8qefSNVMhzAKBggqhkjOPhxvquwvdyu5
CQYDVQQGEwJVUzESMBAGA1UEChMJSW50ZXJuZXQyMSEwHwYDVQQDExhJbkNvbW1v
biBFQ0MgU2VydmVyIENBIDIwHhcNMjUwNzE2MDAwMDAwWhcNMjYwNzE2MjM1OTU5
WjBpMQswCQYDVQQGEwJVUzETMBEGA1UECBMKQ2FsaWZvcm5pYTEgMB4GA1UEChMX
RW5lcmd5IFNjaWVuY2VzIE5ldHdvcmsxIzAhBgNVBAMTGnNlYmFzdGlhbjEuYWNt
ZS1kZXYuZXMubmV0MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEl+z2kyLu0aHy
79D457pdQSzWNmqsxg83oz3QHgMoP3lwCGk6G461dvbwrAbC+GMAmmlJiWq6Kg6r
3tHKkrJQ5aOCAykwggMlMB8GA1UdIwQYMBaAFDJfCtkYWe1BcSHV7gni2a+y1w+x
MB0GA1UdDgQWBBRnH5X2pNXqYObRzzZgcRhlBH/YijAOBgNVHQ8BAf8EBAMCB4Aw
DAYDVR0TAQH/BAIwADAdBgNVHSUEFjAUBggrBgEFBQcDAQYIKwYBBQUHAwIwSQYD
VR0gBEIwQDA0BgsrBgEEAbIxAQICZzAlMCMGCCsGAQUFBwIBFhdodHRwczovL3Nl
Y3RpZ28uY29tL0NQUzAIBgZngQwBA2692AYDVR0fBDkwNzA1oDOgMYYvaHR0cDov
L2NybC5zZWN0aWdvLmNvbS9JbkNvbW1vbkVDQ1NlcnZlckNBMi5jcmwwcAYIKwYB
BQUHAQEEZDBiMDsGCCsGAQUFBzAChi9odHRwOi8vY3J0LnNlY3RpZ28uY29tL0lu
Q29tbW9uRUNDU2VydmVyQ0EyLmNydDAjBggrBgEFBQcwAYYXaHR0cDovL29jc3Au
c2VjdGlnby5jb20wJQYDVR0RBB4wHIIac2ViYXN0aWFuMS5hY21lLWRldi5lcy5u
ZXQwggF+BgorBgEEAdZ5AgQCBIIBbgSCAWoBaAB2ANgJVTuUT3r/yBYZb5RPhauw
+Pxeh1UmDxXRLnK7RUsUAAABmBFSahIAAAQDAEcwRQIhALH3c5u5Y6Vns6FhsnNK
JsrL8Fu5qD58fJBHHohL7jKOAiBsXD8Qg+f+RH3Hl7I0G6H0wKWMrGCmM9jyYCsM
XfXXvAB2AKyrMHBs6+yEMfQT0vSRXxEeQiRDsfKmjE88KzunHgLDAAABmBFSac8A
AAQDAEcwRQIhAN3Sd4gWxB0y4aD/0hF4QkbAop6D3tl9t70nFhjvHhLGAiBCT8TQ
Qop++H/BhJcYMVP59BN5ATOBdp4iRNUr/gJL+gB2ANdtfRDRp/V3wsfpX9cAv/mC
yTNaZeHQswFzF8DIxWl3AAABmBFSacsAAAQDAEcwRQIgImeOxwmllsMJHtcH9in5
vTSM+XGMDG/pvHg1Bfyti/QCIQDDzebqT+5OhK0cgNHP0Yyo9IbbFT3hUF5j5ssY
Pn+jCzAKBggqhkjOPQQDAgNIADBFAiEA7UApgH/4lqVIidf6hQt0KS+Wx60I2HoE
oSlzzVurgu0CIFeUruafCMHm2SzuP1eUCgAcMBHtTiugiduq+726bxcw2ln0noLE
-----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 InCommon 🎉

Renewing a certificate

Issuing a certificate is generally not a problem in enterprise environments. But the ability to reliably renew certificates and reload services gracefully post renewal is. I am using the --force flag for renewal only because the default configuration in ACME clients only performs automatic renewal 1 < N < 30 number of days before certificate expiration.

$ ./acme.sh --renew --domain myserver.example.com --force
[Tue 15 Jul 22:50:37 CDT 2025] The domain 'myserver.example.com' seems to already have an ECC cert, let's use it.
[Tue 15 Jul 22:50:37 CDT 2025] Renewing: 'myserver.example.com'
[Tue 15 Jul 22:50:37 CDT 2025] Renewing using Le_API=https://acmeproxy.example.com/acme/acme/directory
[Tue 15 Jul 22:50:38 CDT 2025] Using CA: https://acmeproxy.example.com/acme/acme/directory
[Tue 15 Jul 22:50:38 CDT 2025] Standalone mode.
[Tue 15 Jul 22:50:38 CDT 2025] Single domain='myserver.example.com'
[Tue 15 Jul 22:50:38 CDT 2025] Getting webroot for domain='myserver.example.com'
[Tue 15 Jul 22:50:38 CDT 2025] Verifying: myserver.example.com
[Tue 15 Jul 22:50:38 CDT 2025] Standalone mode server
[Tue 15 Jul 22:50:40 CDT 2025] Success
[Tue 15 Jul 22:50:40 CDT 2025] Verification finished, beginning signing.
[Tue 15 Jul 22:50:40 CDT 2025] Let's finalize the order.
[Tue 15 Jul 22:50:40 CDT 2025] Le_OrderFinalize='https://acmeproxy.example.com/acme/acme/order/qImka7i2D609vh5gLrW6VOwGDoXtd0Mi/finalize'
[Tue 15 Jul 22:50:47 CDT 2025] Downloading cert.
[Tue 15 Jul 22:50:47 CDT 2025] Le_LinkCert='https://acmeproxy.example.com/acme/acme/certificate/f1Am3j0kYAKZa8pl8TXmxvPHoNiBTusU'
[Tue 15 Jul 22:50:48 CDT 2025] Cert success.
-----BEGIN CERTIFICATE-----
MIIE1TCCBHugAwIBAgIQdNISA47bpyNGREPFAKQnljAKBggqhkjOPQQDAjBEMQsw
CQYDVQQGEwJVUzESMBAGA1UEChMJSW50ZXJuZXQyMSEwHwYDVQQDExhJbkNvbW1v
biBFQ0MgU2VydmVyIENBIDIwHhcNMjUwNzE2MDAwMDAwWhcNMjYwNzE2MjM1OTU5
WjBpMQswCQYDVQQGEwJVUzETMBEGA1UECBMKQ2FsaWZvcm5pYTEgMB4GA1UEChMX
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ZS1kZXYuZXMubmV0MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEl+z2kyLu0aHy
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3tHKkrJQ5aOCAygwggMkMB8GA1UdIwQYMBaAFDJfCtkYWe1BcSHV7gni2a+y1w+x
MB0GA1UdDgQWBBRnH5X2pNXqYObRzzZgcRhlBH/YijAOBgNVHQ8BAf8EBAMCB4Aw
DAYDVR0TAQH/BAIwADAdBgNVHSUEFjAUBggrBgEFBQcDAQYIKwYBBQUHAwIwSQYD
VR0gBEIwQDA0BgsrBgEEAbIxAQICZzAlMCMGCCsGAQUFBwIBFhdodHRwczovL3Nl
Y3RpZ28uY29tL0NQUzAIBgZngQwBAgIwQAYDVR0fBDkwNzA1oDOgMYYvaHR0cDov
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Q29tbW9uRUNDU2VydmVyQ0EyLmNydDAjBggrBgEFBQcwAYYXaHR0cDovL29jc3Au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-----END CERTIFICATE-----
[Tue 15 Jul 22:50:48 CDT 2025] Your cert is in: /root/.acme.sh/myserver.example.com_ecc/myserver.example.com.cer
[Tue 15 Jul 22:50:48 CDT 2025] Your cert key is in: /root/.acme.sh/myserver.example.com_ecc/myserver.example.com.key
[Tue 15 Jul 22:50:48 CDT 2025] The intermediate CA cert is in: /root/.acme.sh/myserver.example.com_ecc/ca.cer
[Tue 15 Jul 22:50:48 CDT 2025] And the full-chain cert is in: /root/.acme.sh/myserver.example.com_ecc/fullchain.cer

Cert renewal was a success! ✨

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Solve ACME http-01 challenge without opening port 80 to the internet, obtain certs from an external certificate authority.

Topics

golang certificates acme acme-server step-ca

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Apache-2.0 license
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Release v0.1.1 Latest
Jan 15, 2026
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