diff --git a/src/app/utils/cookies.js b/src/app/utils/cookies.js
index cc64a8e..2f19b1c 100644
--- a/src/app/utils/cookies.js
+++ b/src/app/utils/cookies.js
@@ -2,6 +2,6 @@
 export const forwardCookies = (headers, c) => {
   const setCookieHeaders = headers.getSetCookie?.() || [];
   setCookieHeaders.forEach((cookie) => {
-    c.header("Set-Cookie", cookie);
+    c.header("Set-Cookie", cookie, { append: true });
   });
 };
diff --git a/test/integration/cookie-attributes.test.js b/test/integration/cookie-attributes.test.js
new file mode 100644
index 0000000..bf04c08
--- /dev/null
+++ b/test/integration/cookie-attributes.test.js
@@ -0,0 +1,213 @@
+import { test } from "tap";
+import { Hono } from "hono";
+import { getTestInstance } from "../helpers/test-instance.js";
+import { createApp } from "../../src/app/app.js";
+import { forwardCookies } from "../../src/app/utils/cookies.js";
+import { authorizeParams } from "../helpers/oauth-flow.js";
+
+const SESSION_COOKIE = "better-auth.session_token";
+
+const LOGOUT_COOKIES = [
+  "better-auth.dont_remember",
+  "better-auth.session_data",
+  "better-auth.session_token",
+];
+
+function readSetCookie(headers) {
+  if (!headers) return [];
+  if (typeof headers.getSetCookie === "function") return headers.getSetCookie();
+  if (typeof headers.get === "function") {
+    const value = headers.get("set-cookie");
+    return value ? [value] : [];
+  }
+  if (Array.isArray(headers)) {
+    return headers
+      .filter(([name]) => name.toLowerCase() === "set-cookie")
+      .map(([, value]) => value);
+  }
+  return [];
+}
+
+function cookieNamed(headers, name) {
+  return readSetCookie(headers).find((cookie) => cookie.startsWith(`${name}=`));
+}
+
+function attributes(cookie) {
+  return cookie
+    .split(";")
+    .slice(1)
+    .map((part) => part.trim());
+}
+
+function attributeValue(cookie, name) {
+  const part = attributes(cookie).find(
+    (attribute) => attribute.split("=")[0].toLowerCase() === name.toLowerCase(),
+  );
+  return part?.split("=").slice(1).join("=");
+}
+
+function hasLifetime(cookie) {
+  return Boolean(
+    attributeValue(cookie, "Max-Age") || attributeValue(cookie, "Expires"),
+  );
+}
+
+async function magicLinkHeaders(auth, getMagicLinks, email) {
+  const callbackURL = "http://localhost:3000/profile";
+  await auth.api.signInMagicLink({
+    body: { email, callbackURL },
+    headers: new Headers(),
+  });
+  const magicLink = getMagicLinks().find((link) => link.email === email);
+  if (!magicLink) throw new Error(`No magic link found for ${email}`);
+
+  try {
+    const result = await auth.api.magicLinkVerify({
+      query: { token: magicLink.token, callbackURL },
+      headers: new Headers(),
+      returnHeaders: true,
+    });
+    return result.headers;
+  } catch (error) {
+    if (error.statusCode !== 302) throw error;
+    if (!error.headers) {
+      throw new Error("magicLinkVerify redirected without headers", {
+        cause: error,
+      });
+    }
+    return error.headers;
+  }
+}
+
+test("session cookie keeps its security attributes on magic-link verification", async (t) => {
+  const instance = await getTestInstance(t);
+  const headers = await magicLinkHeaders(
+    instance.auth,
+    instance.getMagicLinks,
+    "cookie-attributes@example.com",
+  );
+  const cookie = cookieNamed(headers, SESSION_COOKIE);
+
+  t.ok(cookie, "session cookie is set");
+  t.equal(attributeValue(cookie, "HttpOnly"), "", "HttpOnly is set");
+  t.equal(attributeValue(cookie, "SameSite"), "Lax", "SameSite=Lax is set");
+  t.equal(attributeValue(cookie, "Path"), "/", "Path=/ is set");
+  t.ok(hasLifetime(cookie), "session cookie has a lifetime");
+});
+
+test("authorize response sets no cookie", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "authorize-cookie@example.com",
+  );
+
+  // OAuth state travels in a signed query string (sig=), not in a cookie.
+  const params = authorizeParams({ state: "authorize-cookie" });
+  const res = await app.request(
+    `/api/auth/oauth2/authorize?${params.toString()}`,
+    { headers: { cookie: sessionCookie } },
+  );
+
+  t.equal(res.status, 302, "authorize redirects to the callback");
+  t.same(readSetCookie(res.headers), [], "no cookie is set");
+});
+
+test("logout clears every better-auth cookie", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "logout-cookies@example.com",
+  );
+
+  const res = await app.request("/logout", {
+    method: "POST",
+    headers: { cookie: sessionCookie },
+  });
+
+  t.equal(res.status, 302, "redirects after logout");
+  const names = readSetCookie(res.headers)
+    .map((cookie) => cookie.split("=")[0])
+    .sort();
+  t.same(names, LOGOUT_COOKIES, "forwards one clearing cookie per cookie");
+});
+
+test("logout clearing cookies keep their attributes", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "logout-attributes@example.com",
+  );
+
+  const res = await app.request("/logout", {
+    method: "POST",
+    headers: { cookie: sessionCookie },
+  });
+  const cookies = readSetCookie(res.headers);
+
+  t.equal(cookies.length, LOGOUT_COOKIES.length, "every cookie is forwarded");
+  for (const cookie of cookies) {
+    const name = cookie.split("=")[0];
+    t.equal(attributeValue(cookie, "Max-Age"), "0", `${name} expires now`);
+    t.equal(attributeValue(cookie, "Path"), "/", `${name} keeps Path=/`);
+    t.equal(attributeValue(cookie, "HttpOnly"), "", `${name} keeps HttpOnly`);
+    t.equal(
+      attributeValue(cookie, "SameSite"),
+      "Lax",
+      `${name} keeps SameSite=Lax`,
+    );
+  }
+});
+
+test("GET /logout clears every better-auth cookie", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "logout-get@example.com",
+  );
+
+  const res = await app.request("/logout", {
+    headers: { cookie: sessionCookie },
+  });
+
+  t.equal(res.status, 302, "redirects after logout");
+  const names = readSetCookie(res.headers)
+    .map((cookie) => cookie.split("=")[0])
+    .sort();
+  t.same(names, LOGOUT_COOKIES, "forwards one clearing cookie per cookie");
+});
+
+test("forwardCookies keeps a Set-Cookie already on the response", async (t) => {
+  const app = new Hono();
+  app.get("/forward", (c) => {
+    c.header("Set-Cookie", "existing=1; Path=/");
+    const headers = new Headers();
+    headers.append("set-cookie", "first=1; Path=/; HttpOnly");
+    headers.append("set-cookie", "second=2; Path=/; HttpOnly");
+    forwardCookies(headers, c);
+    return c.body(null);
+  });
+
+  const cookies = readSetCookie((await app.request("/forward")).headers);
+
+  t.equal(cookies.length, 3, "no header is replaced or duplicated");
+  t.match(cookies[0], /^existing=1/, "the existing cookie stays first");
+  t.match(cookies[1], /^first=1/, "the first forwarded cookie follows");
+  t.match(cookies[2], /^second=2/, "the second forwarded cookie follows");
+});
+
+test("logout redirects when signOut returns no headers", async (t) => {
+  const instance = await getTestInstance(t);
+  const auth = {
+    api: {
+      getSession: async () => null,
+      signOut: async () => ({}),
+    },
+  };
+  const app = createApp(auth, instance.db);
+
+  const res = await app.request("/logout");
+
+  t.equal(res.status, 302, "redirects despite the missing headers");
+  t.same(readSetCookie(res.headers), [], "sets no cookie");
+});