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/**
* Authentication of callers of the MCP server over Streamable HTTP.
*
* Modes:
* - `none`: local development only; the server refuses to bind a
* non-loopback address in this mode.
* - `static-bearer`: pre-shared bearer tokens mapped to named principals.
* This does NOT implement MCP OAuth discovery/authorization; it suits
* clients that let you configure an Authorization header.
* - `oauth`: OAuth 2.0 resource server per the MCP authorization
* specification: RFC 9728 protected resource metadata, Bearer challenges,
* and token validation (issuer, audience/resource, expiry, scopes) via a
* configured JWKS or RFC 7662 introspection at an external authorization
* server.
*
* Every protected request is authenticated; session identifiers are never
* treated as credentials, and tokens are only accepted in the Authorization
* header.
*
* @module server/authentication
*/
import crypto from "node:crypto";
import {
type AuthInfo,
OAuthError,
OAuthErrorCode,
type OAuthTokenVerifier,
bearerAuthChallengeResponse,
getOAuthProtectedResourceMetadataUrl,
verifyBearerToken,
} from "@modelcontextprotocol/server";
import * as jose from "jose";
import type { Config } from "../config.js";
import type { SecretResolver } from "../util/secrets.js";
import { OagMcpError } from "../errors.js";
import type { Logs } from "../logging/logger.js";
import type { SecretRegistry } from "../util/redact.js";
import type { Principal } from "../types.js";
import { trimTrailingSlashes } from "../util/path.js";
import { opaquePrincipalId } from "./authorization.js";
/** Result of authenticating a request. */
export type AuthResult =
| { ok: true; principal: Principal; authInfo: AuthInfo }
| { ok: false; response: Response };
/** Authenticator for HTTP requests. */
export interface HttpAuthenticator {
readonly mode: "none" | "static-bearer" | "oauth";
/** Authenticate one request. */
authenticate(req: Request, logs: Logs): Promise<AuthResult>;
/** Serve discovery metadata, or undefined when the path is not metadata. */
metadata(req: Request): Response | undefined;
}
/** Error carrying a machine-readable token validation reason. */
class TokenRejected extends OAuthError {
constructor(
readonly reason: string,
message: string,
) {
super(OAuthErrorCode.InvalidToken, message);
}
}
/**
* Parse scopes from token claims (`scope` string or `scp` array/string).
*
* @param {Object} claims - token claims
* @return {Array} scopes
*/
export function scopesFromClaims(claims: Record<string, unknown>): string[] {
const raw = claims.scope ?? claims.scp;
if (Array.isArray(raw)) {
return raw.map(String);
}
if (typeof raw === "string") {
return raw.split(/\s+/).filter(Boolean);
}
return [];
}
/** Reasons for jose errors, by error class; the first match wins. */
const JOSE_REASONS: ReadonlyArray<
[abstract new (...args: never[]) => Error, string]
> = [
[jose.errors.JWTExpired, "expired"],
[jose.errors.JWSSignatureVerificationFailed, "invalid_signature"],
[jose.errors.JWKSNoMatchingKey, "unknown_signing_key"],
[jose.errors.JOSEAlgNotAllowed, "algorithm_not_allowed"],
[jose.errors.JWSInvalid, "malformed_token"],
[jose.errors.JWTInvalid, "malformed_token"],
];
/** Reasons for failed JWT claim checks, by claim. */
const CLAIM_REASONS: Readonly<Record<string, string>> = {
aud: "audience_mismatch",
iss: "issuer_mismatch",
nbf: "not_yet_valid",
};
/**
* Map jose errors to stable reasons.
*
* @private
*/
function _joseReason(err: unknown): string {
if (
err instanceof jose.errors.JWTClaimValidationFailed &&
!(err instanceof jose.errors.JWTExpired)
) {
return Object.hasOwn(CLAIM_REASONS, err.claim)
? CLAIM_REASONS[err.claim]
: `claim_${err.claim}_invalid`;
}
return (
JOSE_REASONS.find(([cls]) => err instanceof cls)?.[1] ?? "invalid_token"
);
}
/**
* Whether a host binds only to loopback.
*
* @param {String} host - bind host
* @return {Boolean} true for loopback
*/
export function isLoopbackHost(host: string): boolean {
return (
["127.0.0.1", "localhost", "::1", "[::1]"].includes(host) ||
host.startsWith("127.")
);
}
/**
* Discover the JWKS URI from authorization server metadata.
*
* @private
*/
async function _discoverJwks(issuer: string): Promise<string> {
const u = new URL(issuer);
const pathPart = trimTrailingSlashes(u.pathname);
const candidates = [
`${u.origin}/.well-known/oauth-authorization-server${pathPart}`,
`${trimTrailingSlashes(issuer)}/.well-known/openid-configuration`,
];
for (const url of candidates) {
try {
const res = await fetch(url, { redirect: "error" });
if (!res.ok) {
continue;
}
const meta = (await res.json()) as Record<string, unknown>;
if (meta.issuer !== issuer) {
throw new OagMcpError(
"MCP_AUTH_ISSUER_MISMATCH",
`Authorization server metadata at ${url} reports issuer ${String(meta.issuer)}, expected ${issuer}`,
);
}
if (typeof meta.jwks_uri === "string") {
return meta.jwks_uri;
}
} catch (err) {
if (err instanceof OagMcpError) {
throw err;
}
}
}
throw new OagMcpError(
"MCP_AUTH_JWKS_UNKNOWN",
`Could not discover jwks_uri for issuer ${issuer}`,
{
hint: "Set mcpAuth.oauth.jwksUri explicitly, or configure introspection.",
},
);
}
/**
* JWT access token verifier using a remote JWKS.
*/
class JwtVerifier implements OAuthTokenVerifier {
private readonly jwks: ReturnType<typeof jose.createRemoteJWKSet>;
constructor(
jwksUri: string,
private readonly o: {
issuer: string;
audiences: string[];
algorithms: string[];
clockToleranceSec: number;
resource: URL;
},
) {
this.jwks = jose.createRemoteJWKSet(new URL(jwksUri), {
timeoutDuration: 5000,
cooldownDuration: 30000,
});
}
async verifyAccessToken(token: string): Promise<AuthInfo> {
let payload: jose.JWTPayload;
try {
({ payload } = await jose.jwtVerify(token, this.jwks, {
issuer: this.o.issuer,
audience: this.o.audiences,
algorithms: this.o.algorithms,
clockTolerance: this.o.clockToleranceSec,
requiredClaims: ["exp"],
}));
} catch (err) {
throw new TokenRejected(_joseReason(err), "The access token is invalid");
}
const claims = payload as Record<string, unknown>;
return {
token,
clientId: String(
claims.client_id ?? claims.azp ?? claims.sub ?? "unknown",
),
scopes: scopesFromClaims(claims),
expiresAt: payload.exp,
resource: this.o.resource,
extra: { sub: payload.sub, iss: payload.iss },
};
}
}
/** An introspection response that passed the checks. */
type ActiveToken = Record<string, unknown> & { exp: number };
/**
* The audiences of an introspection response's `aud`.
*
* @private
*/
function _audiences(aud: unknown): string[] {
if (Array.isArray(aud)) {
return aud.map(String);
}
return aud ? [String(aud)] : [];
}
/**
* RFC 7662 token introspection verifier for opaque tokens.
*/
class IntrospectionVerifier implements OAuthTokenVerifier {
constructor(
private readonly o: {
endpoint: string;
clientId: string;
clientSecret: string;
issuer: string;
audiences: string[];
resource: URL;
},
) {}
async verifyAccessToken(token: string): Promise<AuthInfo> {
const data = await this._introspect(token);
this._check(data);
return {
token,
clientId: String(data.client_id ?? data.sub ?? "unknown"),
scopes: scopesFromClaims(data),
expiresAt: data.exp,
resource: this.o.resource,
extra: { sub: data.sub, iss: data.iss ?? this.o.issuer },
};
}
/**
* Ask the introspection endpoint about a token.
*
* @private
*/
private async _introspect(token: string): Promise<Record<string, unknown>> {
let res: Response;
try {
res = await fetch(this.o.endpoint, {
method: "POST",
redirect: "error",
headers: {
"content-type": "application/x-www-form-urlencoded",
accept: "application/json",
authorization: `Basic ${Buffer.from(`${encodeURIComponent(this.o.clientId)}:${encodeURIComponent(this.o.clientSecret)}`).toString("base64")}`,
},
body: new URLSearchParams({ token, token_type_hint: "access_token" }),
signal: AbortSignal.timeout(5000),
});
} catch {
throw new OAuthError(
OAuthErrorCode.ServerError,
"Token introspection is unavailable",
);
}
if (!res.ok) {
throw new OAuthError(
OAuthErrorCode.ServerError,
"Token introspection failed",
);
}
return (await res.json()) as Record<string, unknown>;
}
/**
* Check that a token is active, ours and unexpired.
*
* @private
*/
private _check(data: Record<string, unknown>): asserts data is ActiveToken {
if (data.active !== true) {
throw new TokenRejected("inactive", "The access token is not active");
}
if (data.iss !== undefined && data.iss !== this.o.issuer) {
throw new TokenRejected(
"issuer_mismatch",
"The access token was issued by another issuer",
);
}
if (!_audiences(data.aud).some((a) => this.o.audiences.includes(a))) {
throw new TokenRejected(
"audience_mismatch",
"The access token is not intended for this server",
);
}
if (typeof data.exp !== "number" || data.exp * 1000 < Date.now()) {
throw new TokenRejected("expired", "The access token has expired");
}
}
}
/**
* Timing-safe comparison of two strings via their digests.
*
* @private
*/
function _safeEqual(a: string, b: string): boolean {
const da = crypto.createHash("sha256").update(a).digest();
const db = crypto.createHash("sha256").update(b).digest();
return crypto.timingSafeEqual(da, db);
}
/**
* Bearer token from an Authorization header.
*
* @private
*/
function _bearer(req: Request): string | undefined {
const h = req.headers.get("authorization");
const m = h ? /^Bearer\s+([^\s]+)\s*$/i.exec(h) : null;
return m ? m[1] : undefined;
}
/**
* JSON error response with a WWW-Authenticate challenge.
*
* @private
*/
function _challenge(
status: number,
error: string | undefined,
description: string,
): Response {
const params = [`realm="oag-mcp"`];
if (error) {
params.push(`error="${error}"`, `error_description="${description}"`);
}
return new Response(
JSON.stringify({
error: error ?? "unauthorized",
error_description: description,
}),
{
status,
headers: {
"content-type": "application/json",
"www-authenticate": `Bearer ${params.join(", ")}`,
},
},
);
}
/** Options for {@link createHttpAuthenticator}. */
export interface AuthenticatorOptions {
config: Config;
resolver: SecretResolver;
registry: SecretRegistry;
logs: Logs;
/** Public URL of the MCP endpoint (the protected resource). */
resourceUrl: URL;
resourceName: string;
}
/** A configured static bearer token with its resolved value. */
type StaticEntry = NonNullable<
Config["mcpAuth"]["staticBearer"]
>["tokens"][number] & { value: string };
/** OAuth resource server settings. */
type OAuthConfig = NonNullable<Config["mcpAuth"]["oauth"]>;
/** What an OAuth authenticator checks tokens against. */
interface OAuthContext {
o: OAuthConfig;
verifier: OAuthTokenVerifier;
validation: "jwt" | "introspection";
resource: URL;
resourceMetadataUrl: string;
registry: SecretRegistry;
/** The HMAC key for opaque principal ids. */
principalIdKey: crypto.BinaryLike;
}
/**
* Create the HTTP authenticator for the configured mode.
*
* @param {Object} opts - options
* @return {Promise} authenticator
*/
export async function createHttpAuthenticator(
opts: AuthenticatorOptions,
): Promise<HttpAuthenticator> {
const mode = opts.config.mcpAuth.mode;
if (mode === "none") {
return _noneAuthenticator(opts.logs);
}
if (mode === "static-bearer") {
return _staticBearerAuthenticator(opts);
}
return _oauthAuthenticator(opts);
}
/**
* Local development: every caller is anonymous.
*
* @private
*/
function _noneAuthenticator(logs: Logs): HttpAuthenticator {
const mode = "none";
logs.audit(
"authentication.mode_configured",
"success",
{
mode,
warning: "unauthenticated; loopback only",
},
"warn",
);
return {
mode,
metadata: () => undefined,
authenticate: async (_req, l) => {
const principal: Principal = {
id: "anonymous",
kind: "anonymous",
scopes: [],
};
l.audit("authentication.succeeded", "success", {
mode,
principalId: principal.id,
});
return {
ok: true,
principal,
authInfo: {
token: "",
clientId: "anonymous",
scopes: [],
extra: { principal },
},
};
},
};
}
/**
* Pre-shared bearer tokens mapped to named principals.
*
* @private
*/
function _staticBearerAuthenticator(
opts: AuthenticatorOptions,
): HttpAuthenticator {
const mode = "static-bearer";
const entries = _staticEntries(opts);
opts.logs.audit("authentication.mode_configured", "success", {
mode,
principals: entries.map((e) => e.principal),
note: "static bearer does not implement MCP OAuth discovery",
});
return {
mode,
metadata: () => undefined,
authenticate: async (req, l) => _authenticateStatic(req, l, entries),
};
}
/**
* Resolve the configured static bearer tokens, refusing weak ones.
*
* @private
*/
function _staticEntries(opts: AuthenticatorOptions): StaticEntry[] {
const tokens = opts.config.mcpAuth.staticBearer?.tokens;
if (!tokens || tokens.length === 0) {
throw new OagMcpError(
"MCP_AUTH_CONFIG_INVALID",
"mcpAuth.mode is static-bearer but mcpAuth.staticBearer.tokens is empty",
);
}
return tokens.map((t) => {
const value = opts.resolver.resolve(
t.token,
`mcpAuth token for ${t.principal}`,
);
if (value.length < 16) {
throw new OagMcpError(
"MCP_AUTH_TOKEN_WEAK",
`Static bearer token for ${t.principal} is shorter than 16 characters`,
{ hint: "Generate one with: openssl rand -hex 32" },
);
}
opts.registry.add(value);
return { ...t, value };
});
}
/**
* The entry a token belongs to, comparing against every entry to keep
* timing independent of position.
*
* @private
*/
function _matchStatic(
token: string,
entries: StaticEntry[],
): StaticEntry | undefined {
let match: StaticEntry | undefined;
for (const e of entries) {
if (_safeEqual(token, e.value) && !match) {
match = e;
}
}
return match;
}
/**
* Audit a refused static bearer request and challenge the caller.
*
* @private
*/
function _refuseStatic(
l: Logs,
reason: string,
response: Response,
): AuthResult {
l.audit(
"authentication.failed",
"failure",
{ mode: "static-bearer", reason },
"warn",
);
return { ok: false, response };
}
/**
* Authenticate a request with a static bearer token.
*
* @private
*/
function _authenticateStatic(
req: Request,
l: Logs,
entries: StaticEntry[],
): AuthResult {
const token = _bearer(req);
if (!token) {
return _refuseStatic(
l,
"missing_token",
_challenge(401, undefined, "Bearer token required"),
);
}
const match = _matchStatic(token, entries);
if (!match) {
return _refuseStatic(
l,
"invalid_token",
_challenge(401, "invalid_token", "The bearer token is invalid"),
);
}
const principal: Principal = {
id: `static:${match.principal}`,
kind: "static",
name: match.principal,
scopes: match.scopes,
};
l.audit("authentication.succeeded", "success", {
mode: "static-bearer",
principalId: principal.id,
});
return {
ok: true,
principal,
authInfo: {
token: "[static-bearer]",
clientId: match.principal,
scopes: match.scopes,
extra: { principal },
},
};
}
/**
* The OAuth settings, refusing a missing section or an insecure issuer.
*
* @private
*/
function _oauthConfig(config: Config): OAuthConfig {
const o = config.mcpAuth.oauth;
if (!o) {
throw new OagMcpError(
"MCP_AUTH_CONFIG_INVALID",
"mcpAuth.mode is oauth but mcpAuth.oauth is not configured",
);
}
const issuerUrl = new URL(o.issuer);
if (
issuerUrl.protocol !== "https:" &&
!o.allowInsecureIssuer &&
!isLoopbackHost(issuerUrl.hostname)
) {
throw new OagMcpError(
"MCP_AUTH_ISSUER_INSECURE",
`OAuth issuer ${o.issuer} must use HTTPS`,
{
hint: "Use an HTTPS issuer; allowInsecureIssuer is for local testing only.",
},
);
}
return o;
}
/**
* The token verifier: introspection when configured, otherwise JWTs signed
* by the issuer's JWKS.
*
* @private
*/
async function _oauthVerifier(
o: OAuthConfig,
opts: AuthenticatorOptions,
audiences: string[],
resource: URL,
): Promise<Pick<OAuthContext, "verifier" | "validation">> {
if (o.introspection) {
const clientId = opts.resolver.resolve(
o.introspection.clientId,
"introspection client id",
);
const clientSecret = opts.resolver.resolve(
o.introspection.clientSecret,
"introspection client secret",
);
opts.registry.add(clientSecret);
return {
verifier: new IntrospectionVerifier({
endpoint: o.introspection.endpoint,
clientId,
clientSecret,
issuer: o.issuer,
audiences,
resource,
}),
validation: "introspection",
};
}
const jwksUri = o.jwksUri ?? (await _discoverJwks(o.issuer));
return {
verifier: new JwtVerifier(jwksUri, {
issuer: o.issuer,
audiences,
algorithms: o.algorithms,
clockToleranceSec: o.clockToleranceSec,
resource,
}),
validation: "jwt",
};
}
/**
* Serve RFC 9728 protected resource metadata at its well-known paths.
*
* @private
*/
function _metadataHandler(
prm: Record<string, unknown>,
paths: Set<string>,
): HttpAuthenticator["metadata"] {
return (req) => {
if (!paths.has(new URL(req.url).pathname)) {
return undefined;
}
if (req.method !== "GET" && req.method !== "HEAD") {
return new Response(null, {
status: 405,
headers: { allow: "GET, HEAD" },
});
}
return new Response(JSON.stringify(prm), {
status: 200,
headers: {
"content-type": "application/json",
"cache-control": "max-age=300",
},
});
};
}
/** The shortest accepted `mcpAuth.oauth.principalIdKey`. */
const MIN_PRINCIPAL_ID_KEY_LENGTH = 32;
/**
* The HMAC key for opaque OAuth principal ids: the configured
* `principalIdKey`, or without one a random key for this process only, so
* ids stay private but change on every restart.
*
* @private
*/
function _principalIdKey(
o: OAuthConfig,
opts: AuthenticatorOptions,
): crypto.BinaryLike {
if (!o.principalIdKey) {
return crypto.randomBytes(32);
}
const key = opts.resolver.resolve(
o.principalIdKey,
"mcpAuth.oauth.principalIdKey",
);
if (key.length < MIN_PRINCIPAL_ID_KEY_LENGTH) {
throw new OagMcpError(
"MCP_AUTH_PRINCIPAL_KEY_WEAK",
`mcpAuth.oauth.principalIdKey is shorter than ${MIN_PRINCIPAL_ID_KEY_LENGTH} characters`,
{ hint: "Generate one with: openssl rand -hex 32" },
);
}
opts.registry.add(key);
return key;
}
/**
* OAuth 2.0 resource server.
*
* @private
*/
async function _oauthAuthenticator(
opts: AuthenticatorOptions,
): Promise<HttpAuthenticator> {
const mode = "oauth";
const o = _oauthConfig(opts.config);
const resource = new URL(o.resource ?? opts.resourceUrl.toString());
const audiences =
o.audience && o.audience.length > 0 ? o.audience : [resource.toString()];
const resourceMetadataUrl = getOAuthProtectedResourceMetadataUrl(resource);
const { verifier, validation } = await _oauthVerifier(
o,
opts,
audiences,
resource,
);
const metadata = _metadataHandler(
{
resource: resource.toString(),
authorization_servers: [o.issuer],
scopes_supported: o.scopesSupported ?? o.requiredScopes,
bearer_methods_supported: ["header"],
resource_name: opts.resourceName,
},
new Set([
"/.well-known/oauth-protected-resource",
new URL(resourceMetadataUrl).pathname,
]),
);
const principalIdKey = _principalIdKey(o, opts);
opts.logs.audit(
"authentication.mode_configured",
"success",
{
mode,
validation,
issuer: o.issuer,
requiredScopes: o.requiredScopes,
...(o.principalIdKey
? {}
: {
warning:
"mcpAuth.oauth.principalIdKey is not set; principal ids change on every restart",
}),
},
o.principalIdKey ? "info" : "warn",
);
const ctx: OAuthContext = {
o,
verifier,
validation,
resource,
resourceMetadataUrl,
registry: opts.registry,
principalIdKey,
};
return {
mode,
metadata,
authenticate: (req, l) => _authenticateOAuth(req, l, ctx),
};
}
/**
* Authenticate a request with an OAuth access token.
*
* @private
*/
async function _authenticateOAuth(
req: Request,
l: Logs,
ctx: OAuthContext,
): Promise<AuthResult> {
const { o, validation, resourceMetadataUrl } = ctx;
try {
const authInfo = await verifyBearerToken(req.headers.get("authorization"), {
verifier: ctx.verifier,
requiredScopes: o.requiredScopes,
resourceMetadataUrl,
expectedResource: ctx.resource,
});
const extra = (authInfo.extra ?? {}) as { sub?: string; iss?: string };
const principal: Principal = {
id: opaquePrincipalId(
"oauth",
[String(extra.iss ?? o.issuer), String(extra.sub ?? authInfo.clientId)],
ctx.principalIdKey,
),
kind: "oauth",
clientId: authInfo.clientId,
scopes: authInfo.scopes,
expiresAt: authInfo.expiresAt,
};
ctx.registry.add(authInfo.token);
l.audit("authentication.succeeded", "success", {
mode: "oauth",
validation,
principalId: principal.id,
scopeCount: principal.scopes.length,
});
return {
ok: true,
principal,
authInfo: { ...authInfo, extra: { ...authInfo.extra, principal } },
};
} catch (err) {
l.audit(
"authentication.failed",
"failure",
{ mode: "oauth", validation, reason: _oauthFailureReason(err, req) },
"warn",
);
return {
ok: false,
response: bearerAuthChallengeResponse(err, {
requiredScopes: o.requiredScopes,
resourceMetadataUrl,
}),
};
}
}
/**
* A stable reason for a refused OAuth request.
*
* @private
*/
function _oauthFailureReason(err: unknown, req: Request): string {
if (err instanceof TokenRejected) {
return err.reason;
}
if (!req.headers.get("authorization")) {
return "missing_token";
}
const code = err instanceof OAuthError ? err.code : "server_error";
if (code === OAuthErrorCode.InsufficientScope) {
return "insufficient_scope";
}
const message = String((err as Error).message);
if (/expired/i.test(message)) {
return "expired";
}
return /resource/i.test(message) ? "resource_mismatch" : String(code);
}
|