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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 end-to-end demo, sidecar, TPM setup, mock services, and registry helper scripts live in the split demo repository. The demo pins a gateway image such as ghcr.io/TODO_ORG/TODO_IMAGE:TODO_TAG and does not require this source checkout.

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.

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.