agent_gateway

An mTLS HTTP/2 CONNECT proxy that authorizes connections based on custom X.509 certificate extensions.

The proxy accepts incoming mTLS connections, extracts a custom extension value from the client certificate, and checks a PostgreSQL-backed signed permission registry to decide whether the client may connect to the requested destination. If allowed, it opens a raw TCP connection to the destination and tunnels data bidirectionally. The client is responsible for establishing its own TLS session to the destination through the tunnel.

Building

cargo build --release

The sidecar uses a simulated TPM identity. Install the native TPM stack before building or running it:

sudo apt-get install libtss2-dev swtpm tpm2-tools pkg-config

Quick start

./demo/setup.sh

The setup script generates demo TLS material, creates config.toml when needed, starts Postgres and static HTTPS mock services with Podman Compose or Docker Compose, applies the database migration, builds and starts the gateway, enrolls a demo principal, grants access to docstore and messaging, creates a demo agent handle, and verifies that Claude Code can fetch https://docstore/health through the gateway.

demo/generate-server-certs.sh creates gateway TLS material (server-ca.pem, server.pem, ...) and mock HTTPS service TLS material (mock-ca.pem, mock-services.pem, ...). The local demo enrolls with ./demo/demo-agent.sh, which starts a local swtpm, creates a persistent P-256 signing key in that simulated TPM, and prepares machine-client.pem as a certificate carrier for that public key and identity extension. The gateway does not trust a client CA bundle; it authorizes the exact subject public key recorded in signed Postgres permission rows.

demo/setup.sh keeps its tpm2-pkcs11 state under the demo state directory by default. Override AGENT_GATEWAY_DEMO_TPM2_PKCS11_STORE only when you intentionally want the demo principal to use another store.

After setup, prompt the demo agent:

./demo/demo-agent.sh prompt agent-alpha \
  --prompt "Use the Bash tool to run exactly these commands: curl -sS https://docstore/documents and curl -sS https://messaging/messages. Then summarize what you found."

On later runs, start the gateway first and use ./demo/demo-agent.sh prompt. ./demo/connect.sh prepares machine-client.pem for the current simulated TPM key and identity extension whenever it prepares or starts the sidecar. --regenerate-certs creates a fresh simulated TPM state; any permissions for the old subject key will no longer match.

Pass a custom policy extension value: ./demo/connect.sh start-sidecar ... --extension-value agent-beta. The extension value must match permission_registry.subject_identity in an active signed permission row.

The simulated TPM state lives under $AGENT_STATE/client/swtpm/. By default, the sidecar uses TCTI swtpm:host=127.0.0.1,port=2321 and persistent handle 0x81010004; override the handle or simulator data port with ./demo/connect.sh start-sidecar --tpm-handle and --swtpm-port. The swtpm control port is always the data port plus one, which matches the TSS swtpm TCTI convention.

Configuration

Copy config.example.toml to config.toml and edit it. Key sections:

[server] -- Listen address and TLS material.

Field	Required	Description
listen_addr	yes	host:port to bind (e.g. 0.0.0.0:8443)
tls_cert_path	yes	PEM server certificate
tls_key_path	yes	PEM private key for the server cert

[policy] -- Configures the certificate identity extension and Postgres registry access.

Field	Description
client_ext_oid	OID of the custom X.509 extension to extract (dotted notation)
database_url	Postgres URL for the authorization registry. Prefer database_url_env outside local development.
database_url_env	Environment variable containing the Postgres URL.
max_connections	Maximum Postgres pool connections. Defaults to 5.
connect_timeout_ms	Postgres connection timeout. Defaults to 5000.
pool_acquire_timeout_ms	Pool acquire timeout per authorization check. Defaults to 1000.
query_timeout_ms	Query timeout per registry lookup. Defaults to 500.

[observability] -- Logging and tracing.

Field	Required	Description
log_level	yes	tracing filter (e.g. info, debug, agent_gateway=debug)
otlp_endpoint	no	OTLP gRPC endpoint for distributed tracing

Set AGENT_GATEWAY_LOG_STDOUT=false to disable stdout/stderr formatting while leaving OTLP export enabled. The sidecar reads observability settings from environment variables. Use RUST_LOG for its tracing filter and set OTEL_EXPORTER_OTLP_ENDPOINT (for example, http://localhost:4317) to export sidecar spans over OTLP. When enabled, the sidecar injects W3C trace-context headers into the CONNECT request it sends to the gateway, and the gateway continues the same trace.

Running

agent_gateway --config config.toml

Run migrations explicitly before starting the gateway:

psql "$AGENT_GATEWAY_DATABASE_URL" -f migrations/0001_signed_authorization_registry.sql

Gateway startup verifies the authorization registry schema version and fails fast if the database is not migrated. The runtime gateway database role should be read-only for authorization tables; use a separate admin role for migrations and registry writes.

Shut down cleanly with Ctrl-C.

Register a principal signing key from the TPM owner machine with:

./registry-cli/register-principal-key.sh org-alice

The script creates or reuses a non-exportable TPM-backed P-256 key through tpm2_ptool and PKCS#11, stores only the public key in principal_signing_keys, and uses the friendly key_id (org-alice, org-bob, etc.) for the registry row. Run it on the machine that owns the TPM, with AGENT_GATEWAY_DATABASE_URL or DATABASE_URL pointing at Postgres.

For a manual demo without ./demo/setup.sh, use three windows:

# Principal shell: enroll the principal TPM public key.
./registry-cli/register-principal-key.sh org-alice

# Admin shell: grant destination delegation authority to that principal.
./registry-cli/grant-principal-scope.sh org-alice docstore messaging api.anthropic.com

# Principal shell: create a local agent handle with initial signed permissions.
AGENT_HANDLE="$(./demo/demo-agent.sh create \
  --identity agent-alpha \
  --grant docstore \
  --grant messaging)"

# Principal shell: send the first prompt through that agent.
./demo/demo-agent.sh prompt "$AGENT_HANDLE" \
  --prompt "Access https://docstore/documents with curl."

Authorization Registry

The gateway authorizes a CONNECT only when all of these checks pass:

1. The mTLS client certificate has the configured UTF8String identity extension.
2. The requested authority normalizes to a host:port destination.
3. Postgres contains an active permission_registry row for that identity, destination, and the leaf certificate's exact SubjectPublicKeyInfo DER.
4. The row's signature verifies over the canonical permission row fields with the referenced active principal signing key.
5. principal_key_permissions confirms that the signing key was allowed to delegate that destination.

Database Structure

The authorization registry has three main tables:

Table	Key Columns	Purpose
principal_signing_keys	key_id, algorithm, public_key_spki_der, not_before, not_after, revoked_at	Stores trusted P-256 public keys that may sign permissions.
principal_key_permissions	signing_key_id, destination, not_before, not_after, revoked_at	Defines which destinations each signing key is allowed to delegate.
permission_registry	permission_id, signing_key_id, subject_identity, subject_public_key_spki_der, destination, not_before, not_after, revoked_at, signature	Stores signed permissions that authorize a subject identity and exact subject key to reach a normalized destination.

principal_key_permissions.signing_key_id and permission_registry.signing_key_id both reference principal_signing_keys.key_id. A permission is usable only when the permission row is active, the signing key is active, the signature verifies over the canonical row fields, and the signing key has a matching destination delegation row.

The signed bytes are the following UTF-8 text, with fields in this exact order and timestamps formatted as UTC RFC 3339 with six fractional digits:

agent-gateway-permission-v1
permission_id=perm-1
signing_key_id=org-alice
subject_identity=agent-alpha
subject_public_key_spki_der=3059301306072a8648ce3d020106082a8648ce3d03010703420004...
destination=api.example.com:443
not_before=2026-05-01T00:00:00.000000Z
not_after=2026-06-01T00:00:00.000000Z

Destination strings are normalized with the same rules used for CONNECT requests: hostnames are lowercased, omitted ports default to 443, and IPv6 destinations use bracketed host:port form.

Client requirements

Clients must:

1. Connect over HTTP/2 with mTLS. Present a structurally valid client certificate and prove possession of the certificate private key during the TLS handshake. The certificate must contain a custom X.509 extension at the OID configured in policy.client_ext_oid, with a DER-encoded UTF8String value. The full leaf SubjectPublicKeyInfo DER must match an active signed permission row.

2. Use the HTTP CONNECT method. The request authority must be host:port (port defaults to 443 if omitted). Example using hyper:

   let req = Request::builder()
       .method(Method::CONNECT)
       .uri("api.example.com:443")
       .body(Empty::<Bytes>::new())?;

3. Handle TLS to the destination. After receiving 200 OK, the tunnel is an opaque TCP pipe. The client must perform its own TLS handshake with the destination through the tunnel.

Response codes

Status	Meaning
200	Tunnel established -- begin sending data
400	Malformed request (missing/invalid authority)
403	Policy denied the connection
405	Non-CONNECT method used
502	Could not reach the destination

Client certificate extension

The extension value is matched exactly (case-sensitive) against signed permission rows. The extension must be an X.509 extension at the configured OID containing a single DER-encoded ASN.1 UTF8String.

Example certificate generation with rcgen:

use rcgen::{CertificateParams, CustomExtension};

let oid: &[u64] = &[1, 3, 6, 1, 4, 1, 57264, 1, 1];
let value = der_encode_utf8_string("agent-alpha");
params.custom_extensions.push(
    CustomExtension::from_oid_content(oid, value),
);

Tests

cargo test

Database-backed policy and e2e tests require TEST_DATABASE_URL to point at a Postgres database that the test process can migrate and write to. The tests cover policy evaluation, signed-permission verification, signer delegation scope enforcement, destination normalization, config validation, TLS PKI generation, and proxy request parsing.