diff --git a/.changeset/vercel-basic-auth-callbacks.md b/.changeset/vercel-basic-auth-callbacks.md
new file mode 100644
index 0000000..9a15e03
--- /dev/null
+++ b/.changeset/vercel-basic-auth-callbacks.md
@@ -0,0 +1,5 @@
+---
+"@plainbrew/vercel-basic-auth": minor
+---
+
+feat: add `beforeAuth` and `afterAuth` callback options to `basicAuth`
diff --git a/packages/vercel-basic-auth/src/index.test.ts b/packages/vercel-basic-auth/src/index.test.ts
index 5e3e6d5..bf49702 100644
--- a/packages/vercel-basic-auth/src/index.test.ts
+++ b/packages/vercel-basic-auth/src/index.test.ts
@@ -1,4 +1,4 @@
-import { afterEach, describe, expect, test } from "vitest";
+import { afterEach, describe, expect, test, vi } from "vitest";
 
 import { basicAuth } from "./index";
 
@@ -194,3 +194,67 @@ describe("認証ヘッダーのバリデーション", () => {
     expect(res?.status).toBe(401);
   });
 });
+
+describe("beforeAuth コールバック", () => {
+  test("beforeAuth が false を返すとき 401 を返す", () => {
+    const req = makeRequest(makeBasicAuthHeader(USERNAME, PASSWORD));
+    const res = basicAuth(req, {
+      username: USERNAME,
+      password: PASSWORD,
+      beforeAuth: () => false,
+    });
+    expect(res?.status).toBe(401);
+  });
+
+  test("beforeAuth が true を返すとき通常の認証フローに進む", () => {
+    const req = makeRequest(makeBasicAuthHeader(USERNAME, PASSWORD));
+    expect(
+      basicAuth(req, { username: USERNAME, password: PASSWORD, beforeAuth: () => true }),
+    ).toBeNull();
+  });
+
+  test("beforeAuth が false を返すとき認証ヘッダーなしでも 401 を返す", () => {
+    const req = makeRequest();
+    const res = basicAuth(req, {
+      username: USERNAME,
+      password: PASSWORD,
+      beforeAuth: () => false,
+    });
+    expect(res?.status).toBe(401);
+  });
+
+  test("NODE_ENV=development (dev=false) のときも beforeAuth は呼ばれる", () => {
+    process.env.NODE_ENV = "development";
+    const beforeAuth = vi.fn(() => false);
+    const req = makeRequest();
+    const res = basicAuth(req, { username: USERNAME, password: PASSWORD, beforeAuth });
+    expect(beforeAuth).toHaveBeenCalled();
+    expect(res?.status).toBe(401);
+  });
+});
+
+describe("afterAuth コールバック", () => {
+  test("afterAuth が false を返すとき 401 を返す", () => {
+    const req = makeRequest(makeBasicAuthHeader(USERNAME, PASSWORD));
+    const res = basicAuth(req, {
+      username: USERNAME,
+      password: PASSWORD,
+      afterAuth: () => false,
+    });
+    expect(res?.status).toBe(401);
+  });
+
+  test("afterAuth が true を返すとき null を返す", () => {
+    const req = makeRequest(makeBasicAuthHeader(USERNAME, PASSWORD));
+    expect(
+      basicAuth(req, { username: USERNAME, password: PASSWORD, afterAuth: () => true }),
+    ).toBeNull();
+  });
+
+  test("認証失敗のとき afterAuth は呼ばれない", () => {
+    const afterAuth = vi.fn(() => true);
+    const req = makeRequest(makeBasicAuthHeader(USERNAME, "wrong"));
+    basicAuth(req, { username: USERNAME, password: PASSWORD, afterAuth });
+    expect(afterAuth).not.toHaveBeenCalled();
+  });
+});
diff --git a/packages/vercel-basic-auth/src/index.ts b/packages/vercel-basic-auth/src/index.ts
index 1d26aff..d025369 100644
--- a/packages/vercel-basic-auth/src/index.ts
+++ b/packages/vercel-basic-auth/src/index.ts
@@ -13,6 +13,18 @@ export type BasicAuthOptions = {
    * @default false
    */
   dev?: boolean;
+  /**
+   * 組み込みの環境判定後、認証チェック前に呼ばれるコールバック
+   * - true を返すと通常の認証フローに進む
+   * - false を返すと認証失敗 (401) を返す
+   */
+  beforeAuth?: (request: Request) => boolean;
+  /**
+   * 認証成功後に呼ばれるコールバック
+   * - true を返すと通過する
+   * - false を返すと認証失敗 (401) を返す
+   */
+  afterAuth?: (request: Request) => boolean;
 };
 
 export function basicAuth(
@@ -22,6 +34,8 @@ export function basicAuth(
     password: authPassword,
     vercelEnvTarget = "only-production",
     dev = false,
+    beforeAuth,
+    afterAuth,
   }: BasicAuthOptions,
 ): Response | null {
   function unauthorized() {
@@ -33,6 +47,10 @@ export function basicAuth(
     });
   }
 
+  if (beforeAuth && !beforeAuth(request)) {
+    return unauthorized();
+  }
+
   if (process.env.NODE_ENV === "development") {
     if (!dev) {
       return null;
@@ -79,5 +97,9 @@ export function basicAuth(
     return unauthorized();
   }
 
+  if (afterAuth && !afterAuth(request)) {
+    return unauthorized();
+  }
+
   return null;
 }