diff --git a/app/mywhoosh/client.py b/app/mywhoosh/client.py
new file mode 100644
index 0000000..5711ce9
--- /dev/null
+++ b/app/mywhoosh/client.py
@@ -0,0 +1,69 @@
+from __future__ import annotations
+
+import uuid
+
+import httpx
+
+from app.mywhoosh.models import MyWhooshToken
+from app.mywhoosh.tokenstore import MyWhooshTokenStore
+
+LOGIN_URL = "https://services.mywhoosh.com/http-service/api/login"
+ACTIVITIES_BASE = "https://service14.mywhoosh.com/v2/"
+
+
+class MyWhooshError(RuntimeError):
+    pass
+
+
+class MyWhooshAuthError(MyWhooshError):
+    pass
+
+
+class MyWhooshTransientError(MyWhooshError):
+    pass
+
+
+class MyWhooshIntegrationError(MyWhooshError):
+    pass
+
+
+class MyWhooshClient:
+    def __init__(self, token_store: MyWhooshTokenStore, http_client: httpx.AsyncClient | None = None) -> None:
+        self.token_store = token_store
+        self.http = http_client or httpx.AsyncClient(timeout=30.0)
+        self.token = token_store.load()
+
+    async def login(self, email: str, password: str) -> None:
+        payload = {
+            "Username": email,
+            "Password": password,
+            "Platform": "Android",
+            "Action": 1001,
+            "CorrelationId": str(uuid.uuid4()),
+            "DeviceId": str(uuid.uuid4()),
+            "Authorization": "",
+        }
+        try:
+            response = await self.http.post(LOGIN_URL, json=payload)
+        except httpx.TransportError as exc:
+            raise MyWhooshTransientError("MyWhoosh login request failed") from exc
+        if response.status_code >= 500:
+            raise MyWhooshTransientError(f"MyWhoosh login returned HTTP {response.status_code}")
+        if response.status_code >= 400:
+            raise MyWhooshAuthError(f"MyWhoosh login returned HTTP {response.status_code}")
+        try:
+            body = response.json()
+        except ValueError as exc:
+            raise MyWhooshIntegrationError("MyWhoosh login returned invalid JSON") from exc
+        if body.get("Success") is not True or not body.get("AccessToken"):
+            raise MyWhooshAuthError(str(body.get("Message") or "MyWhoosh login failed"))
+        self.token = MyWhooshToken(
+            access_token=str(body["AccessToken"]),
+            refresh_token=str(body["RefreshToken"]) if body.get("RefreshToken") else None,
+            whoosh_id=str(body["WhooshId"]) if body.get("WhooshId") else None,
+        )
+        self.token_store.save(self.token)
+
+    async def ensure_authenticated(self, email: str, password: str) -> None:
+        if self.token is None:
+            await self.login(email, password)
diff --git a/pyproject.toml b/pyproject.toml
index 35b7ee0..f7197af 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -15,12 +15,13 @@ dependencies = [
   "jinja2>=3.1,<4",
   "python-multipart>=0.0.9,<1",
   "itsdangerous>=2.1,<3",
+  "httpx>=0.27,<1",
 ]
 
 [project.optional-dependencies]
 test = [
   "pytest>=8,<9",
-  "httpx>=0.27,<1",
+  "pytest-asyncio>=0.24,<1",
 ]
 
 [tool.setuptools.packages]
diff --git a/tests/mywhoosh/test_client_auth.py b/tests/mywhoosh/test_client_auth.py
new file mode 100644
index 0000000..bb8ef10
--- /dev/null
+++ b/tests/mywhoosh/test_client_auth.py
@@ -0,0 +1,39 @@
+import httpx
+import pytest
+
+from app.mywhoosh.client import MyWhooshClient, MyWhooshAuthError
+from app.mywhoosh.models import MyWhooshToken
+from app.mywhoosh.tokenstore import MyWhooshTokenStore
+
+
+@pytest.mark.asyncio
+async def test_login_saves_access_refresh_and_whoosh_id(tmp_path) -> None:
+    async def handler(request: httpx.Request) -> httpx.Response:
+        assert request.url.path == "/http-service/api/login"
+        return httpx.Response(
+            200,
+            json={
+                "Success": True,
+                "AccessToken": "new-access",
+                "RefreshToken": "new-refresh",
+                "WhooshId": "w-1",
+            },
+        )
+
+    store = MyWhooshTokenStore(tmp_path / "mywhoosh.json")
+    client = MyWhooshClient(store, http_client=httpx.AsyncClient(transport=httpx.MockTransport(handler)))
+    await client.login("rider@example.com", "secret")
+    assert store.load() == MyWhooshToken("new-access", "new-refresh", "w-1")
+
+
+@pytest.mark.asyncio
+async def test_invalid_credentials_raise_auth_error(tmp_path) -> None:
+    async def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(200, json={"Success": False, "Message": "Invalid credentials"})
+
+    client = MyWhooshClient(
+        MyWhooshTokenStore(tmp_path / "mywhoosh.json"),
+        http_client=httpx.AsyncClient(transport=httpx.MockTransport(handler)),
+    )
+    with pytest.raises(MyWhooshAuthError):
+        await client.login("rider@example.com", "bad")