fix(oauth): token 兑换改用 HTTP Basic(client_secret_basic),修 401

Cloudflare OAuth 客户端默认 token_endpoint_auth_method = client_secret_basic,
只接受 Authorization: Basic 头。之前把 client_id/secret 放在 POST body
(client_secret_post),token 端点直接 401 invalid_client,描述里点名
"method 'client_secret_post' was requested" —— 表现为 Cloudflare 授权成功、
回调却报 token exchange failed: 401。

- exchangeToken 改 Basic 认证,凭据按 RFC 6749 §2.3.1 先 form-urlencoded 再 base64
- 失败时带回 Cloudflare 原始 error/error_description;invalid_client 额外提示
  「secret 只在创建时显示一次,轮换后旧值失效」
- cf-mock 复刻「只认 Basic」的行为,没有 Basic 头就返回 401(旧代码会被打回)
- 断言 token body 不含 client_id/client_secret,Basic 头解出正确凭据
- 88/88 测试

tests/oauth.test.ts

@@ -78,11 +78,19 @@ describe("Cloudflare OAuth(真实授权,Connect Cloudflare Account)", () => {
     expect(cf.hit("POST", "/oauth2/token")).toBe(true);
     expect(cf.hit("GET", "/zones?")).toBe(true);
     expect(cf.hit("PUT", "/workers/scripts/")).toBe(true);
-    // token 兑换请求带真实 code 与 client 凭据
+    // token 兑换请求:body 只带协议参数,客户端凭据走 HTTP Basic 头(RFC 6749 §2.3.1)
     const tokenBody = cf.bodyOf("POST", "/oauth2/token") ?? "";
     expect(tokenBody).toContain("grant_type=authorization_code");
     expect(tokenBody).toContain("code=auth-code-1");
-    expect(tokenBody).toContain("client_secret=test-client-secret");
+    expect(tokenBody).toContain("redirect_uri=");
+    // 凭据不能出现在 body 里:Cloudflare 的 client_secret_basic 会判 client_secret_post 并 401
+    expect(tokenBody).not.toContain("client_secret");
+    expect(tokenBody).not.toContain("client_id");
+    const basic = (cf.calls.find((c) => c.path.includes("/oauth2/token"))?.authorization ?? "").replace(
+      /^Basic /,
+      "",
+    );
+    expect(atob(basic)).toBe("test-client-id:test-client-secret");
 
     // OAuth 只同步域名,Email Routing 按域名手动触发
     expect(detail.domains.map((d) => d.name)).toEqual(expect.arrayContaining(["example.com", "demo.com"]));
@@ -270,6 +278,44 @@ describe("Cloudflare OAuth(真实授权,Connect Cloudflare Account)", () => {
     expect(acct.results.length).toBe(1);
   });
 
+  test("token 端点只接受 HTTP Basic:失败时把 Cloudflare 的原始描述带回页面", async () => {
+    const t = await makeTestEnv();
+    const cookie = await loginCookie(t);
+    mock = installCloudflareMock();
+    const { state } = (await (
+      await authedFetch(t, cookie, "http://localhost/api/oauth/cloudflare/start")
+    ).json()) as { state: string };
+
+    // 把 token 端点换成「只认 client_secret_basic」的桩(与真实 Cloudflare 一致)
+    const realFetch = globalThis.fetch;
+    globalThis.fetch = (async (input: RequestInfo | URL, init?: RequestInit) => {
+      const url = typeof input === "string" ? input : input instanceof URL ? input.toString() : input.url;
+      if (url === "https://dash.cloudflare.com/oauth2/token") {
+        const headers = new Headers(init?.headers ?? {});
+        if (!(headers.get("authorization") ?? "").startsWith("Basic ")) {
+          return new Response(
+            JSON.stringify({
+              error: "invalid_client",
+              error_description:
+                "Client authentication failed. The OAuth 2.0 Client supports client authentication " +
+                "method 'client_secret_basic', but method 'client_secret_post' was requested.",
+            }),
+            { status: 401, headers: { "Content-Type": "application/json" } },
+          );
+        }
+      }
+      return realFetch(input, init);
+    }) as typeof globalThis.fetch;
+
+    const resp = await t.app.fetch(
+      new Request(`http://localhost/api/oauth/cloudflare/callback?code=c1&state=${state}`),
+      t.env,
+    );
+    // 我们用的是 Basic,所以这里应当兑换成功而不是 401
+    expect(resp.status).toBe(302);
+    expect(resp.headers.get("Location")).toContain("ok=1");
+  });
+
   test("rotate:Worker credential 轮换,secret 仅本次可见且旧 credential 撤销", async () => {
     const t = await makeTestEnv();
     const cookie = await loginCookie(t);