Authentication

vgi-rpc provides built-in authentication factories for common strategies. Each factory returns an AuthenticateFn that you pass to createHttpHandler. You can also combine multiple strategies with chainAuthenticate.

AuthContext

Every authenticate callback returns an AuthContext on success:

import { AuthContext } from "@query-farm/vgi-rpc";

const ctx = new AuthContext(
  "mtls",        // domain — identifies the auth method
  true,          // authenticated
  "alice",       // principal — the identity
  { role: "admin" }, // claims — arbitrary metadata
);

Handlers access the context via ctx.auth:

handler: (params, ctx) => {
  ctx.auth.requireAuthenticated(); // throws if not authenticated
  return { user: ctx.auth.principal };
},

Bearer token

Custom validation

For API keys, opaque tokens, or tokens validated against an external service:

import { bearerAuthenticate, AuthContext } from "@query-farm/vgi-rpc";

const auth = bearerAuthenticate({
  validate: (token) => {
    const user = db.getUserByApiKey(token);
    if (!user) throw new Error("Invalid API key");
    return new AuthContext("apikey", true, user.name, { role: user.role });
  },
});

Static token map

For development, testing, or a small number of pre-shared keys. Uses constant-time comparison:

import { bearerAuthenticateStatic, AuthContext } from "@query-farm/vgi-rpc";

const auth = bearerAuthenticateStatic({
  tokens: {
    "key-abc123": new AuthContext("apikey", true, "alice"),
    "key-def456": new AuthContext("apikey", true, "bob", { role: "admin" }),
  },
});

Accepts Record<string, AuthContext> or ReadonlyMap<string, AuthContext>.

JWT

Validates JWT tokens using OIDC discovery. Requires the oauth4webapi peer dependency.

import { jwtAuthenticate } from "@query-farm/vgi-rpc";

const auth = jwtAuthenticate({
  issuer: "https://auth.example.com",
  audience: "https://api.example.com/vgi",
});

Option	Type	Default	Description
issuer	string	required	Expected iss claim (used for OIDC discovery)
audience	string | string[]	required	Expected aud claim
jwksUri	string	—	Explicit JWKS URL (discovered from issuer if omitted)
principalClaim	string	"sub"	JWT claim to use as principal
domain	string	"jwt"	AuthContext.domain value

When audience is an array, each value is tried in order until one validates — useful when a single endpoint accepts tokens minted for several audiences.

Mutual TLS (mTLS)

For proxy-terminated mTLS connections where the reverse proxy forwards client certificate information in HTTP headers. Two approaches are supported:

• PEM-in-header — the proxy forwards the URL-encoded PEM certificate (e.g., nginx X-SSL-Client-Cert, AWS ALB X-Amzn-Mtls-Clientcert)
• XFCC — the proxy forwards an Envoy x-forwarded-client-cert structured header

Header spoofing

The reverse proxy must strip client-supplied certificate headers before forwarding. These factories trust the header unconditionally. No certificate chain validation is performed — that is the proxy’s responsibility.

Subject CN (simplest)

Extracts the Subject Common Name as principal and populates claims with the DN, serial number, and expiry:

import { mtlsAuthenticateSubject } from "@query-farm/vgi-rpc";

const auth = mtlsAuthenticateSubject({
  allowedSubjects: new Set(["my-service", "other-service"]),
  checkExpiry: true,
});

Option	Type	Default	Description
header	string	"X-SSL-Client-Cert"	Header containing URL-encoded PEM
domain	string	"mtls"	AuthContext.domain value
allowedSubjects	ReadonlySet<string> | null	null	Restrict accepted CNs (null = accept any)
checkExpiry	boolean	false	Reject expired or not-yet-valid certificates

The returned AuthContext has these claims:

Claim	Description
subject_dn	Full DN string (e.g., "CN=my-service")
serial	Serial number as hex string
not_valid_after	Expiry as ISO 8601 string

Fingerprint lookup

Maps certificate fingerprints to pre-configured identities. Useful when you have a known set of client certificates:

import { mtlsAuthenticateFingerprint, AuthContext } from "@query-farm/vgi-rpc";

const auth = mtlsAuthenticateFingerprint({
  fingerprints: {
    "a1b2c3d4...": new AuthContext("mtls", true, "service-a"),
    "e5f6a7b8...": new AuthContext("mtls", true, "service-b", { env: "prod" }),
  },
  algorithm: "sha256", // default; also supports sha1, sha384, sha512
});

Fingerprints must be lowercase hex without colons. Throws at construction time if the algorithm is unsupported.

Option	Type	Default	Description
fingerprints	Record<string, AuthContext> | ReadonlyMap<string, AuthContext>	required	Fingerprint-to-context map
header	string	"X-SSL-Client-Cert"	Header containing URL-encoded PEM
algorithm	string	"sha256"	Hash algorithm
checkExpiry	boolean	false	Reject expired certificates

Custom validation

For full control over certificate inspection:

import { mtlsAuthenticate, AuthContext } from "@query-farm/vgi-rpc";
import type { X509Certificate } from "node:crypto";

const auth = mtlsAuthenticate({
  validate: (cert: X509Certificate) => {
    // Inspect cert.subject, cert.issuer, cert.serialNumber, etc.
    return new AuthContext("mtls", true, "my-principal", {});
  },
  header: "X-Amzn-Mtls-Clientcert", // AWS ALB header
  checkExpiry: true,
});

Option	Type	Default	Description
validate	CertValidateFn	required	Receives X509Certificate, returns AuthContext or throws
header	string	"X-SSL-Client-Cert"	Header containing URL-encoded PEM
checkExpiry	boolean	false	Check validity period before calling validate

XFCC (Envoy)

Parses the x-forwarded-client-cert structured header set by Envoy proxy. Does not require certificate parsing — works with the structured fields directly:

import { mtlsAuthenticateXfcc } from "@query-farm/vgi-rpc";

const auth = mtlsAuthenticateXfcc();
// Extracts CN from Subject field as principal

With custom validation:

import { mtlsAuthenticateXfcc, AuthContext } from "@query-farm/vgi-rpc";
import type { XfccElement } from "@query-farm/vgi-rpc";

const auth = mtlsAuthenticateXfcc({
  validate: (element: XfccElement) => {
    if (element.hash !== "expected-hash") throw new Error("Unknown client");
    return new AuthContext("xfcc", true, "trusted-service", {});
  },
  selectElement: "first", // "first" (original client) or "last" (nearest proxy)
});

Option	Type	Default	Description
validate	XfccValidateFn	—	Custom validation (default: extract CN from Subject)
domain	string	"mtls"	AuthContext.domain value
selectElement	"first" | "last"	"first"	Which element to use when multiple are present

Chaining authenticators

Accept multiple authentication methods on the same endpoint with chainAuthenticate. Authenticators are tried in order — credential errors (plain Error) fall through to the next; other exceptions propagate immediately.

import {
  chainAuthenticate,
  mtlsAuthenticateSubject,
  bearerAuthenticateStatic,
  AuthContext,
} from "@query-farm/vgi-rpc";

const auth = chainAuthenticate(
  mtlsAuthenticateSubject({ allowedSubjects: new Set(["my-service"]) }),
  bearerAuthenticateStatic({
    tokens: { "sk-ci-bot": new AuthContext("apikey", true, "ci-bot") },
  }),
);

const handler = createHttpHandler(protocol, {
  tokenKey: myKey,
  authenticate: auth,
});

When a request arrives with a client certificate header, mTLS is tried first. If the header is missing, the chain falls through to bearer token authentication.

Scenario	Exception type	Result
Credentials accepted	(none)	Returns AuthContext, stops chain
Bad / missing credentials	Plain Error	Tries next authenticator
Authenticated but forbidden	Error with name === "PermissionError"	Propagates immediately
Bug in authenticator	TypeError, RangeError, etc.	Propagates immediately

Cookie-based auth

cookieAuthenticate wraps any inner authenticator so it can also accept the bearer token from a browser cookie (default name _vgi_auth) rather than only the Authorization header. It reads the cookie, rewrites the request with an Authorization: Bearer <token> header, and delegates to the inner authenticator:

const auth = cookieAuthenticate(jwtAuthenticate({ issuer, audience }));

This is what powers the browser session cookie set by the OAuth PKCE flow. cookieAuthenticate lives in the library’s http module (it is not re-exported from the package root).

OAuth

For interactive, browser-based sign-in, vgi-rpc can serve RFC 9728 OAuth Protected Resource Metadata, run the PKCE authorization-code redirect flow, handle the /_oauth/* routes, and emit WWW-Authenticate challenges. See the OAuth guide for the full setup, including the device-code flow and how the cookie session described above is issued.

Wiring it up

Pass any authenticate callback to createHttpHandler:

import { Protocol, createHttpHandler, float } from "@query-farm/vgi-rpc";

const protocol = new Protocol("MyService");
protocol.unary("add", {
  params: { a: float, b: float },
  result: { result: float },
  handler: ({ a, b }) => ({ result: a + b }),
});

const handler = createHttpHandler(protocol, {
  tokenKey: myKey,
  authenticate: auth, // any AuthenticateFn from above
});

Bun.serve({ port: 8080, fetch: handler });

tokenKey is the XChaCha20-Poly1305 master key (32 bytes) used to seal stream-state tokens; a random key is generated if omitted. Supply your own when tokens must survive a restart or be shared across load-balanced workers.

Unauthenticated requests receive a 401 Unauthorized response.