infrabroker

Infrastructure access broker for AI agents — SSH & Kubernetes. The model never touches a credential. (formerly ssh-broker)

The agent requests an action — run a command on a host, query or change a cluster. infrabroker checks it against policy, executes it with a credential minted for that single operation — an ephemeral, scope-limited SSH certificate from its own CA, or a short-lived bound ServiceAccount token — and returns only the output. Keys, certificates and tokens live in the broker's memory and are discarded after the call: nothing enters the model's context, so a prompt-injected agent has nothing to exfiltrate.

Three frontends share the same engine (internal/broker) and tool surface (internal/mcpserver):

• MCP stdio (local, recommended for personal use) — cmd/mcp-broker. Tools: ssh_execute, ssh_session_open / ssh_session_exec / ssh_session_close, ssh_list_servers, ssh_put_file / ssh_get_file; with clusters configured, also k8s_get / k8s_list / k8s_logs / k8s_apply / k8s_delete / k8s_list_clusters. No transport auth — isolation comes from the process being launched by the user (as the MCP spec recommends for stdio).
• MCP HTTP + OAuth2/OIDC (remote, multi-user) — cmd/mcp-broker-http, Streamable HTTP. Same tools, but each client authenticates with an OIDC bearer token validated locally against the issuer's JWKS; the user identity (and groups, for per-user RBAC) is propagated to the signer.
• HTTP + mTLS — cmd/broker, POST /v1/ssh_run (one-shot), for network agents authenticated with a client certificate.

Documentation

This README is a landing page. The detail lives in focused, single-source docs:

Document	Contents
ARCHITECTURE.md	Diagram, request flow, design decisions, sudo elevation, sessions, multi-CA
THREAT_MODEL.md	Actors, trust boundaries, security controls, and explicit non-goals/gaps
OPERATIONS.md	Runbook: startup, adding hosts, hot-reload, broker-ctl, PKI rotation, configs
API.md	HTTP endpoint reference for all services
USAGE.md	Guide to the MCP tools (SSH + Kubernetes), dry-run, and audit review (for the model / operator)
SECURITY.md	Vulnerability disclosure policy
CONTRIBUTING.md · CODING_STYLE.md	Workflow, versioning, Go style

Why infrabroker

• Anti-exfiltration (prompt injection): the ephemeral key/cert/token live only in the broker's memory; they never enter the model's context.
• Kubernetes without kubeconfigs: the signer mints a short-lived bound ServiceAccount token (TokenRequest API) per operation; every cluster is default-deny with per-verb/resource/namespace policy and the same dry-run, approval and audit path as SSH.
• Anti-reuse: each cert carries a TTL of minutes, source-address (broker or bastion IP), and — for one-shot — a force-command. Useless outside its host/time/IP.
• Controlled escalation: allow_sudo / allowed_sudo_users live in the signer; a compromised broker cannot escalate where policy forbids it.
• CA compromise bounded: one CA per host group (ca_keys), each key optionally in Azure Key Vault — the private key never leaves the HSM.
• Audit / non-repudiation: append-only, Ed25519-chained log correlated by serial across signer, broker, and sshd.

The full threat model — including what the system deliberately does not defend — is in THREAT_MODEL.md.

How it works

AI model ──tool call──> broker ──mTLS──> [control-plane] ──mTLS──> signer
   (no credential)      (ephemeral key      (approval +          (CA key +
                         in RAM, never        guardrails,          policy + RBAC,
                         on disk)             no CA key)           signs the cert)
                            │
                            └── SSH with the ephemeral cert ──> bastion ──> target host
                                                                 └─ stdout/stderr/exit_code ─> model

The broker sends an intent ({host, role, purpose, command?, sudo?, pty?, pubkey, …}); the signer derives every certificate constraint from policy and returns the signed cert. The ephemeral private key is generated in the broker and never leaves it. See ARCHITECTURE.md for the request flow, the design decisions, and the per-hop ProxyJump certificate diagrams.

Feature overview

Capability	One-liner	More
Ephemeral certificates	Ed25519 pair in RAM per operation; minutes-long, scoped cert. No reusable secret.	ARCHITECTURE
External signer	A separate cmd/signer holds the CA key and policy; the broker never does.	ARCHITECTURE
Multi-CA + HSM	One CA key per host group via ca_keys; local PEM or Azure Key Vault.	ARCHITECTURE
AI-action firewall	Per-host or composable-by-group command policy (allow/deny/require_approval), POSIX-sh AST parsing, dry-run. Authoritative for one-shot.	ARCHITECTURE · USAGE
Human-in-the-loop approval	Optional control plane gates require_approval commands behind out-of-band approval; the signer enforces it.	ARCHITECTURE · API
Behaviour guardrails	Per-subject anomaly detection (rate, new host, novel command); observe or enforce.	ARCHITECTURE
RBAC	Broker-CN groups (mTLS) + per-end-user OIDC groups; fail-closed.	ARCHITECTURE
sudo / PTY	Policy-gated elevation (sudo -n) and PTY allocation, per host.	ARCHITECTURE
Kubernetes broker	k8s_* tools with per-operation bound SA tokens, default-deny verb/resource/namespace policy, dry-run.	USAGE §10
Session recording	shell/pty sessions to ASCIIcast v2 (.cast), indexed by session_id.	USAGE §8
Chained audit	Append-only, Ed25519-signed, SHA-256-chained; correlated by serial.	USAGE §7 · API
Hot reload	signer.json re-read (and validated) without restart, via POST /v1/reload or SIGHUP.	OPERATIONS §3

Comparison with existing solutions

Several tools address SSH access control or AI-agent credential security, but none cover the full combination that infrabroker targets in a lightweight, self-hosted package.

Feature	infrabroker	Teleport	Vault + SSH engine	StrongDM	ssh-mcp
Ephemeral cert in memory (no disk)	✅	✅	✅	❌	❌
Separate broker / signing service	✅	✅	Partial	❌	❌
MCP-native (AI agents)	✅	✅ (2025)	✅ (2025)	❌	✅
OAuth2/OIDC on MCP transport	✅	✅	✅	❌	❌
Per-command policy + dry-run (AI-action firewall)	✅	❌	❌	❌	❌
Human-in-the-loop approval for AI commands	✅	❌	❌	❌	❌
Per-agent behavioral guardrails (anomaly/rate)	✅	❌	❌	❌	❌
Session recording (ASCIIcast v2, stdin+stdout+stderr)	✅	✅	❌	Partial	❌
Cryptographically chained audit log	✅	❌	❌	Partial	❌
Single-binary / simple self-hosted	✅	❌	❌	❌	✅
HSM/KMS for CA key	✅ (AKV)	✅	✅	—	—

Teleport is the closest commercial equivalent — short-lived SSH certs, RBAC, and since 2025 Secure MCP; its Jan-2026 Agentic Identity Framework targets the same threat model. The difference is operational weight: Teleport needs a dedicated control-plane cluster, recording proxy, and web UI — orders of magnitude heavier than a Go binary + signer.

HashiCorp Vault SSH secrets engine is an SSH CA with full HSM/KMS support and (2025) its own MCP server, but it provides only the signing piece — you still build the execution layer (engine.go, session.go, the MCP tools) yourself.

StrongDM hides credentials but stores long-lived secrets rather than generating ephemeral certs in memory, making it weaker against exfiltration. Smallstep SSH CA is a lightweight OIDC-integrated SSH CA (close to cmd/signer) with no execution broker or MCP layer. ssh-mcp exposes SSH to LLMs over MCP but uses a static SSH key — the exact vulnerability this broker prevents. CyberArk PAM offers comparable JIT cert access but is a closed enterprise platform for human operators, not AI workloads.

Where it fits: MCP-native AI-agent access + in-memory ephemeral certs + separate signer + ASCIIcast recording + chained audit, as a small set of Go binaries without a cluster. Enterprise features (web UI, multi-region HA) are on the roadmap (see HANDOFF.md).

Install

• Prebuilt binaries — each release ships infrabroker_<ver>_{linux,darwin}_{amd64,arm64}.tar.gz with all six binaries, plus the installer tarball (infrabroker-v<ver>.tar.gz) that deploy/install.sh consumes for the systemd production path.
• go install — go install github.com/luisgf/infrabroker/cmd/mcp-broker@latest (pure Go, no CGO; same for the other cmd/ binaries).
• Container — ghcr.io/luisgf/infrabroker (docker or podman, multi-arch; entrypoint is the stdio MCP frontend). See CONTAINERS.md, including a compose demo that runs the full stack against a toy host: cd examples/compose && docker compose up --build -d (or make demo).
• From source — the Quickstart below.

Register with Claude Code in one line — native binary or container:

claude mcp add infrabroker -- ~/bin/mcp-broker -config /secure/path/config.json
claude mcp add infrabroker -- docker run -i --rm -v /secure/path:/config \
  ghcr.io/luisgf/infrabroker -config /config/config.json

Quickstart

# 1. Build (make injects the version from the git tag into every binary)
make install                 # → ~/bin/{signer,broker,broker-ctl,mcp-broker,...}
# or a single binary:        make signer
# (plain `go build ./cmd/...` also works; it reports a dev-<commit> version)

# 2. Start the signing service (must be running before the broker)
./signer.sh start

# 3. Add a host and reload
broker-ctl host add --name web01 --addr web01.example.com:22 --user deploy --scan \
  --groups prod-web --sudo
broker-ctl reload

# (--config is a global flag, before the subcommand; every binary takes --version)
broker-ctl --config /secure/path/signer.json host list
broker-ctl --version            # short; add --verbose for build details

Register the stdio MCP with your client:

// Claude Code — ~/.claude.json
"infrabroker": { "type": "stdio", "command": "/Users/<you>/bin/mcp-broker",
                "args": ["-config", "/secure/path/config.json"] }

// OpenCode — ~/.config/opencode/opencode.json  (note: type "local", command is an array)
"infrabroker": { "type": "local",
                "command": ["/home/<you>/bin/mcp-broker", "-config", "/secure/path/config.json"],
                "enabled": true }

Full setup — local vs external signing mode, the remote OAuth frontend, host fields, sudoers, PKI, and broker-ctl — is in OPERATIONS.md. Tool usage for the model is in USAGE.md.

API

Full reference: API.md.

Service	Endpoint	Auth	Description
Signer	POST /v1/sign	mTLS	Request an ephemeral SSH certificate
Signer	GET /v1/hosts	mTLS	List accessible hosts (filtered by caller groups)
Signer	POST /v1/reload	mTLS	Hot-reload signer.json without restart
Control plane	POST /v1/sign, /v1/approvals/{id}, …	mTLS	Forwarding + human approval
Broker HTTP	POST /v1/ssh_run	mTLS	Execute a one-shot SSH command
MCP HTTP	/.well-known/oauth-protected-resource	None	OAuth2 discovery (RFC 9728)
MCP HTTP	Streamable HTTP	OIDC Bearer	MCP tools

Security

The security posture — trust boundaries, the layered controls (RBAC, command policy, approval gate, guardrails, source-address/TTL pinning, chained audit), and the explicit non-goals (mode=exec sessions are broker-preflighted but not host-enforced, no KRL, secrets logged verbatim, audit fail-open, …) — is documented in THREAT_MODEL.md.

To report a vulnerability, see SECURITY.md. CI enforces gofmt, go vet, go test -race, and govulncheck on every push and PR.

Testing

make test                      # go test -race ./...  (cert build, policy/RBAC/sudo/PTY, hops, …)
bash lab/run_signer_lab.sh     # external signer: broker without ca_key + policy + denial
bash lab/run_mcp_lab.sh        # bastion + target (ProxyJump) MCP scenario
bash lab/run_lab.sh            # HTTP/mTLS frontend

License

Copyright (C) 2026 Luis González Fernández.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License v3.0 as published by the Free Software Foundation. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY. See LICENSE for the full text.