feat: add @plainbrew/vercel-basic-auth package

packages/vercel-basic-auth/.gitignore

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+dist/

packages/vercel-basic-auth/README.md

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+# @plainbrew/vercel-basic-auth
+
+Basic Auth handler for Vercel Edge Middleware.
+
+## Install
+
+```sh
+pnpm add @plainbrew/vercel-basic-auth
+```
+
+## Usage
+
+`proxy.ts`:
+
+```ts
+import { basicAuth } from "@plainbrew/vercel-basic-auth";
+import { NextResponse } from "next/server";
+import type { NextRequest } from "next/server";
+
+export default async function proxy(request: NextRequest) {
+  const basicAuthResponse = basicAuth(request, {
+    username: process.env.BASIC_AUTH_USER ?? "",
+    password: process.env.BASIC_AUTH_PASSWORD ?? "",
+    // vercelEnvTarget: "all", // Apply Basic Auth to all Vercel environments
+    // dev: true, // Apply Basic Auth in local development
+  });
+  if (basicAuthResponse) return basicAuthResponse;
+
+  return NextResponse.next();
+}
+```
+
+## Options
+
+| Option            | Type      | Required | Default             | Description                                |
+| ----------------- | --------- | -------- | ------------------- | ------------------------------------------ |
+| `username`        | `string`  | ✓        |                     | Basic Auth username                        |
+| `password`        | `string`  | ✓        |                     | Basic Auth password                        |
+| `vercelEnvTarget` | `string`  |          | `'only-production'` | Vercel environments to apply Basic Auth    |
+| `dev`             | `boolean` |          | `false`             | Apply Basic Auth in `NODE_ENV=development` |
+
+### `vercelEnvTarget`
+
+| Value             | Behavior                                      |
+| ----------------- | --------------------------------------------- |
+| `only-production` | Apply Basic Auth to Vercel production only    |
+| `all`             | Apply Basic Auth to all Vercel environments   |
+| `disabled`        | Disable Basic Auth on all Vercel environments |
+
+### Notes
+
+- Basic Auth is only applied on Vercel (`VERCEL=1`) by default. Local development is skipped unless `dev: true`.

packages/vercel-basic-auth/package.json

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+{
+  "name": "@plainbrew/vercel-basic-auth",
+  "version": "0.0.0",
+  "description": "Basic Auth handler for Vercel Edge Middleware",
+  "keywords": [
+    "basic-auth",
+    "middleware",
+    "vercel"
+  ],
+  "license": "MIT",
+  "files": [
+    "dist"
+  ],
+  "main": "./dist/index.js",
+  "module": "./dist/index.mjs",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "import": {
+        "types": "./dist/index.d.mts",
+        "default": "./dist/index.mjs"
+      },
+      "require": {
+        "types": "./dist/index.d.ts",
+        "default": "./dist/index.js"
+      }
+    }
+  },
+  "scripts": {
+    "dev": "tsup --watch",
+    "build": "tsup"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "tsup": "^8.0.0",
+    "typescript": "^5.0.0"
+  }
+}

packages/vercel-basic-auth/src/index.ts

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+export type VercelEnvTarget = "only-production" | "all" | "disabled";
+
+export type BasicAuthOptions = {
+  username: string;
+  password: string;
+  /**
+   * Vercel 環境のどの範囲で Basic 認証を適用するか
+   * @default 'only-production'
+   */
+  vercelEnvTarget?: VercelEnvTarget;
+  /**
+   * NODE_ENV=development でも Basic 認証を適用するか
+   * @default false
+   */
+  dev?: boolean;
+};
+
+export function basicAuth(
+  request: Request,
+  {
+    username: authUsername,
+    password: authPassword,
+    vercelEnvTarget = "only-production",
+    dev = false,
+  }: BasicAuthOptions,
+): Response | null {
+  function unauthorized() {
+    return new Response("Auth required", {
+      status: 401,
+      headers: {
+        "WWW-Authenticate": "Basic",
+      },
+    });
+  }
+
+  if (process.env.NODE_ENV === "development") {
+    if (!dev) {
+      return null;
+    }
+  }
+
+  if (process.env.VERCEL === "1") {
+    if (vercelEnvTarget === "disabled") {
+      return null;
+    }
+    if (vercelEnvTarget === "only-production" && process.env.VERCEL_ENV !== "production") {
+      return null;
+    }
+  }
+
+  const authorization = request.headers.get("authorization");
+  if (!authorization) {
+    return unauthorized();
+  }
+
+  const authValue = authorization.split(" ")[1];
+  if (authValue === undefined) {
+    return unauthorized();
+  }
+
+  try {
+    const [username, password] = atob(authValue).split(":");
+    if (username !== authUsername || password !== authPassword) {
+      return unauthorized();
+    }
+  } catch {
+    return unauthorized();
+  }
+
+  return null;
+}

packages/vercel-basic-auth/tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "ES2019",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "lib": ["ES2019", "DOM"],
+    "strict": true,
+    "declaration": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "types": ["node"]
+  },
+  "include": ["src"]
+}

packages/vercel-basic-auth/tsup.config.ts

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+import { defineConfig } from "tsup";
+
+export default defineConfig({
+  entry: ["src/index.ts"],
+  format: ["cjs", "esm"],
+  dts: true,
+  clean: true,
+});