@molecule/api-middleware-cors

CORS middleware for molecule.dev.

Core interface — the implementation is provided via a bond. Install and wire a CORS bond (e.g. @molecule/api-middleware-cors-express, which registers corsFactory via setCorsFactory()) or cors / createCorsMiddleware() throw "No CORS ... bonded" on first use. APP_ORIGIN / SITE_ORIGIN are the conventional env vars for the allowlist (registered as optional secrets by this package).

Auto-generated, AI-first package reference for the molecule.dev ecosystem. It is written to be read by coding agents as much as by people, and is generated from this package's source — edit src/index.ts JSDoc, not this file.

Quick Start

import { createCorsMiddleware } from '@molecule/api-middleware-cors'
// Explicit allowlist from env; credentials on for cookie/bearer auth.
app.use(
  createCorsMiddleware({
    origin: [process.env.APP_ORIGIN, process.env.SITE_ORIGIN].filter(Boolean),
    credentials: true,
  }),
)

Type

middleware

Installation

npm install @molecule/api-middleware-cors @molecule/api-bond @molecule/api-secrets

API

Interfaces

CorsOptions

CORS configuration options.

interface CorsOptions {
  origin?:
    | string
    | string[]
    | boolean
    | RegExp
    | (string | RegExp | null | undefined)[]
    | ((origin: string | undefined, callback: (err: Error | null, allow?: boolean) => void) => void)
  methods?: string | string[]
  allowedHeaders?: string | string[]
  exposedHeaders?: string | string[]
  credentials?: boolean
  maxAge?: number
  preflightContinue?: boolean
  optionsSuccessStatus?: number
}

Types

Middleware

Generic middleware type — framework-agnostic.

type Middleware = (req: unknown, res: unknown, next: (err?: unknown) => void) => void

• req — The request object.
• res — The response object.
• next — The next middleware function.

CorsFactory

Factory function type for creating CORS middleware with custom options.

type CorsFactory = (options: CorsOptions) => Middleware

Functions

setCors(middleware)

Bonds a CORS middleware implementation for use by getCors() and cors.

function setCors(middleware: Middleware): void

• middleware — The middleware function that handles CORS headers.

getCors()

Gets the bonded CORS middleware.

function getCors(): Middleware

Returns: The bonded CORS middleware function.

hasCors()

Checks if a CORS middleware has been bonded.

function hasCors(): boolean

Returns: true if CORS middleware is available.

setCorsFactory(factory)

Bonds a CORS factory for creating middleware with custom options (origins, methods, headers).

function setCorsFactory(factory: CorsFactory): void

• factory — A function that creates CORS middleware from options.

getCorsFactory()

Gets the bonded CORS factory.

function getCorsFactory(): CorsFactory | null

Returns: The factory function, or null if none has been bonded.

cors(req, res, next)

Default CORS middleware that delegates to the bonded implementation.

function cors(req: unknown, res: unknown, next: (err?: unknown) => void): void

• req — The incoming request object.
• res — The response object.
• next — The next middleware function.

Returns: The result of the bonded CORS handler invocation.

createCorsMiddleware(options)

Creates CORS middleware with custom options via the bonded factory.

function createCorsMiddleware(options: CorsOptions): Middleware

• options — CORS options (origins, methods, headers, credentials, etc.).

Returns: A middleware function that handles CORS headers.

Available Providers

Provider	Package
CORS (Express)	@molecule/api-middleware-cors-express

Injection Notes

Requirements

Peer dependencies:

• @molecule/api-bond ^1.0.1
• @molecule/api-secrets ^1.0.1

Environment Variables

• APP_ORIGIN (optional)
• SITE_ORIGIN (optional)
• APP_URL_SCHEME (optional)

Runtime Dependencies

• @molecule/api-bond
• @molecule/api-secrets

CORS decides which browser ORIGINS may call your API (with credentials). Configure an explicit allowlist from env (APP_ORIGIN / SITE_ORIGIN) via CorsOptions``.origin — don't hand-roll Access-Control-* headers.

• origin: '*' with credentials: true is invalid AND insecure. The browser rejects a wildcard on a credentialed (cookie / Authorization) request, and reflecting arbitrary origins with credentials is a CSRF / data-exfiltration hole. For an app that sends the session cookie or a bearer token, set a SPECIFIC origin allowlist + credentials: true.
• Never "fix" a CORS error by reflecting the request origin unconditionally. That disables the protection entirely — add the real origin to the allowlist (env) instead.
• A permissive dev CORS config must NOT ship to production. Loosen only for local dev, behind a dev-only guard; prod stays on the strict allowlist. (Molecule's preview CORS proxy is dev-only and never ships — mirror that discipline.)