diff --git a/console/src/services/cfapi.ts b/console/src/services/cfapi.ts
index 5af48a4..0021e42 100644
--- a/console/src/services/cfapi.ts
+++ b/console/src/services/cfapi.ts
@@ -400,25 +400,72 @@ export async function getCFApi(env: Env): Promise<CFApi> {
   return new RealCFApi(client);
 }
 
+/** # 函数
+ * 生成 HTTP Basic 认证头的内容(RFC 6749 §2.3.1)
+ * 参数: id - 客户端 ID;secret - 客户端密钥
+ * 返回值: base64(`编码后的 id:编码后的 secret`)
+ */
+export function basicAuthValue(id: string, secret: string): string {
+  // 先做 form-urlencoded 编码(Go 的 url.UserPassword 与 RFC 都是这个语义):
+  // encodeURIComponent 不转义 !'()* ,这里补齐成与 unreserved 集一致
+  const enc = (s: string) =>
+    encodeURIComponent(s).replace(/[!'()*]/g, (c) => `%${c.charCodeAt(0).toString(16).toUpperCase()}`);
+  return btoa(`${enc(id)}:${enc(secret)}`);
+}
+
+/** # 函数
+ * 把 token 端点的失败响应翻译成一句可读的说明(取 Cloudflare 的 error / error_description)
+ */
+async function describeTokenError(resp: Response): Promise<string> {
+  const fallback = `HTTP ${resp.status}`;
+  let detail = "";
+  let code = "";
+  try {
+    const body = (await resp.json()) as { error?: string; error_description?: string };
+    code = body.error ?? "";
+    detail = [body.error, body.error_description].filter(Boolean).join(": ");
+  } catch {
+    // 非 JSON 响应,退回状态码
+  }
+  if (!detail) return fallback;
+  // invalid_client 是最常见的失败:凭据不匹配或 secret 已轮换,直接给出可执行提示
+  const hint =
+    code === "invalid_client"
+      ? " —— 请到设置 → Cloudflare 接入 重新填写 Client ID / Client Secret(secret 只在创建时显示一次,轮换后旧值立即失效)"
+      : "";
+  return `${resp.status} ${detail.slice(0, 300)}${hint}`;
+}
+
 /** # 成员变量: Cloudflare API 实现 **/
 export class RealCFApi implements CFApi {
   /** # 成员变量: OAuth 客户端凭据(settings 或 env) **/
   constructor(private client: CFOAuthClient) {}
 
+  /** 用 code 换 access token。
+   *  **认证方式必须是 HTTP Basic(client_secret_basic)**:Cloudflare OAuth 客户端默认
+   *  `token_endpoint_auth_method = client_secret_basic`,若把 client_id/secret 放在 POST body
+   *  (`client_secret_post`)会被拒,返回 401 invalid_client 且描述里点名
+   *  "method 'client_secret_post' was requested"。 */
   async exchangeToken(code: string, redirectUri: string) {
     const resp = await fetch(CF_OAUTH_TOKEN_URL, {
       method: "POST",
-      headers: { "Content-Type": "application/x-www-form-urlencoded" },
+      headers: {
+        "Content-Type": "application/x-www-form-urlencoded",
+        // RFC 6749 §2.3.1:先对 id 与 secret 做 form-urlencoded 编码,再拼成 Basic 头
+        Authorization: `Basic ${basicAuthValue(this.client.clientId, this.client.clientSecret)}`,
+      },
       body: new URLSearchParams({
         grant_type: "authorization_code",
         code,
-        client_id: this.client.clientId,
-        client_secret: this.client.clientSecret,
         redirect_uri: redirectUri,
       }),
     });
-    if (!resp.ok) throw new Error(`cloudflare token exchange failed: ${resp.status}`);
+    if (!resp.ok) {
+      // 带上 Cloudflare 原始的 error / error_description,否则只能看到一个光秃秃的 401
+      throw new Error(`cloudflare token exchange failed: ${await describeTokenError(resp)}`);
+    }
     const data = (await resp.json()) as { access_token: string; expires_in?: number };
+    if (!data.access_token) throw new Error("cloudflare token exchange returned no access_token");
     return { accessToken: data.access_token, expiresIn: data.expires_in ?? 3600 };
   }
 
diff --git a/package.json b/package.json
index 5b2de2b..715ac92 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "wmailhub",
-  "version": "2.3.4",
+  "version": "2.3.5",
   "description": "WmailHub - 基于 Cloudflare Email Workers 的轻量邮件接收与转发平台(Console 直连 Email Worker)",
   "private": true,
   "type": "module",
diff --git a/tests/cf-mock.ts b/tests/cf-mock.ts
index 032fec2..b1820b4 100644
--- a/tests/cf-mock.ts
+++ b/tests/cf-mock.ts
@@ -13,7 +13,7 @@ export interface CfCall {
   url: string;
   /** 路径(去掉 base) **/
   path: string;
-  /** Authorization 头(OAuth Bearer token) **/
+  /** Authorization 头(Cloudflare API 是 OAuth Bearer token;token 端点是 Basic) **/
   authorization: string | null;
   /** 请求体文本(URL 编码或 JSON);multipart 上传记 null **/
   body: string | null;
@@ -122,6 +122,20 @@ export function installCloudflareMock(opts: CfMockOptions = {}): CfMock {
       return new Response(null, { status: 302, headers: { Location: "https://dash.cloudflare.com/login" } });
     }
     if (url === TOKEN_URL) {
+      // 复刻 Cloudflare 的客户端认证要求:只接受 HTTP Basic(client_secret_basic)。
+      // 把 client_id/secret 放进 POST body(client_secret_post)会被 401 invalid_client 拒绝,
+      // 且错误描述会点名 "method 'client_secret_post' was requested"(2026-09-30 线上踩过)。
+      const auth = headers.get("authorization") ?? "";
+      if (!auth.startsWith("Basic ")) {
+        const desc =
+          "Client authentication failed (e.g., unknown client, no client authentication included, " +
+          "or unsupported authentication method). The OAuth 2.0 Client supports client authentication " +
+          "method 'client_secret_basic', but method 'client_secret_post' was requested.";
+        return new Response(JSON.stringify({ error: "invalid_client", error_description: desc }), {
+          status: 401,
+          headers: { "Content-Type": "application/json" },
+        });
+      }
       if ((opts.tokenStatus ?? 200) !== 200) {
         return new Response(JSON.stringify({ error: "invalid_grant" }), { status: opts.tokenStatus });
       }
diff --git a/tests/oauth.test.ts b/tests/oauth.test.ts
index a59a726..1374ad1 100644
--- a/tests/oauth.test.ts
+++ b/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);