`step-ca` is an online certificate authority for secure, automated certificate management. It's the server counterpart to the [`step` CLI tool](https://github.com/smallstep/cli).
- Issue X.509 certificates for your internal infrastructure:
- HTTPS certificates that [work in browsers](https://smallstep.com/blog/step-v0-8-6-valid-HTTPS-certificates-for-dev-pre-prod.html) ([RFC5280](https://tools.ietf.org/html/rfc5280) and [CA/Browser Forum](https://cabforum.org/baseline-requirements-documents/) compliance)
- TLS certificates for VMs, containers, APIs, mobile clients, database connections, printers, wifi networks, toaster ovens...
- Client certificates to [enable mutual TLS (mTLS)](https://smallstep.com/hello-mtls) in your infra. mTLS is an optional feature in TLS where both client and server authenticate each other. Why add the complexity of a VPN when you can safely use mTLS over the public internet?
- Issue SSH certificates:
- For people, in exchange for single sign-on ID tokens
- For hosts, in exchange for cloud instance identity documents
- Easily automate certificate management:
- It's an ACME v2 server
- It has a JSON API
- It comes with a [Go wrapper](./examples#user-content-basic-client-usage)
- ... and there's a [command-line client](https://github.com/smallstep/cli) you can use in scripts!
Whatever your use case, `step-ca` is easy to use and hard to misuse, thanks to [safe, sane defaults](https://smallstep.com/docs/step-ca/certificate-authority-server-production#sane-cryptographic-defaults).
To get up and running quickly, or as an alternative to running your own `step-ca` server, consider creating a [free hosted smallstep Certificate Manager authority](https://info.smallstep.com/certificate-manager-early-access-mvp/).
- Capable of high availability (HA) deployment using [root federation](https://smallstep.com/blog/step-v0.8.3-federation-root-rotation.html) and/or multiple intermediaries
- [Single-use, short-lived JWK tokens](https://smallstep.com/docs/step-ca/provisioners#jwk) issued by your CD tool — Puppet, Chef, Ansible, Terraform, etc.
ACME is the protocol used by Let's Encrypt to automate the issuance of HTTPS certificates. It's _super easy_ to issue certificates to any ACMEv2 ([RFC8555](https://tools.ietf.org/html/rfc8555)) client.
- Supports the most popular [ACME challenge types](https://letsencrypt.org/docs/challenge-types/):
- For `http-01`, place a token at a well-known URL to prove that you control the web server
- For `dns-01`, add a `TXT` record to prove that you control the DNS record set
- For `tls-alpn-01`, respond to the challenge at the TLS layer ([as Caddy does](https://caddy.community/t/caddy-supports-the-acme-tls-alpn-challenge/4860)) to prove that you control the web server
- Delegate SSH authentication to `step-ca` by using [SSH certificates](https://smallstep.com/blog/use-ssh-certificates/) instead of public keys and `authorized_keys` files
- For user certificates, [connect SSH to your single sign-on provider](https://smallstep.com/blog/diy-single-sign-on-for-ssh/), to improve security with short-lived certificates and MFA (or other security policies) via any OAuth OIDC provider.
- For host certificates, improve security, [eliminate TOFU warnings](https://smallstep.com/blog/use-ssh-certificates/), and set up automated host certificate renewal.
- [Authenticate and obtain a certificate](https://smallstep.com/docs/step-cli/reference/ca/certificate/) using any provisioner supported by `step-ca`
- Securely [distribute root certificates](https://smallstep.com/docs/step-cli/reference/ca/root/) and [bootstrap](https://smallstep.com/docs/step-cli/reference/ca/bootstrap/) PKI relying parties
- [Renew](https://smallstep.com/docs/step-cli/reference/ca/renew/) and [revoke](https://smallstep.com/docs/step-cli/reference/ca/revoke/) certificates issued by `step-ca`
- [Install root certificates](https://smallstep.com/docs/step-cli/reference/certificate/install/) on your machine and browsers, so your CA is trusted
- [Inspect](https://smallstep.com/docs/step-cli/reference/certificate/inspect/) and [lint](https://smallstep.com/docs/step-cli/reference/certificate/lint/) certificates
* Tell us what you like and don't like about managing your PKI - we're eager to help solve problems in this space.
* Tell us about a feature you'd like to see! [Add a feature request Issue](https://github.com/smallstep/certificates/issues/new?assignees=&labels=enhancement%2C+needs+triage&template=enhancement.md&title=), [ask on Discussions](https://github.com/smallstep/certificates/discussions), or hit us up on [Twitter](https://twitter.com/smallsteplabs).
