Introduction

k9-ssh is a lightweight SSH public key retrieval agent that bridges OpenSSH with the Key9 Identity and Access Management (IAM) platform. It enables centralized, passwordless SSH authentication across your fleet without distributing or managing individual authorized_keys files.

How It Works

OpenSSH's AuthorizedKeysCommand directive allows sshd to call an external program at login time to retrieve a user's authorized public keys. k9-ssh implements this interface: when a user attempts to log in, sshd calls k9-ssh with the username, k9-ssh queries the Key9 API, validates each returned key, and prints valid keys to stdout for sshd to evaluate.

User SSH Login
     │
     ▼
sshd (AuthorizedKeysCommand)
     │
     ▼
k9-ssh --user=<username> [--remote=<client-info>]
     │
     ├── Load /opt/k9/etc/k9.yaml
     ├── POST https://ssh-api.k9.io/api/v1/ssh/query/<user>/<group>
     └── Validate & print public keys
     │
     ▼
sshd completes authentication

Key Features

• Centralized key management — public keys live in Key9, not on individual servers

• Machine group scoping — restrict which Key9 users can log in to which groups of machines

• Fail-safe design — errors log silently without exposing key material

• Minimal footprint — ~670 lines of Go, statically compiled, no libc dependency

• Full audit trail — every operation logged to syslog AUTH facility

• Platform portable — Linux, FreeBSD, OpenBSD, NetBSD, Solaris, and more

Supported Platforms

k9-ssh ships as statically compiled binaries for all major Unix-like operating systems and architectures supported by Go, including:

• Linux (amd64, arm64, i386, armv6, armv7, riscv64, and more)

• FreeBSD (amd64, arm64, i386)

• OpenBSD (amd64, arm64)

• NetBSD (amd64, arm64)

• Solaris / illumos (amd64)

• macOS / Darwin (amd64, arm64)

License

k9-ssh is released under the GNU General Public License v2.