prefecthq--fastmcp/tests/server/auth/test_oauth_consent_flow.py

"""Tests for OAuth Proxy consent flow with server-side storage.

This test suite verifies:
1. OAuth transactions are stored in server-side storage (not in-memory)
2. Authorization codes are stored in server-side storage
3. Consent flow redirects correctly through /consent endpoint
4. CSRF protection works with cookies
5. State persists across storage backends
6. Security headers (X-Frame-Options) are set correctly
7. Cookie signing and tampering detection
8. Auto-approve behavior with valid cookies
9. Consent binding cookie prevents confused deputy attacks (GHSA-rww4-4w9c-7733)
"""

import re
import secrets
import time
from urllib.parse import parse_qs, urlparse

import pytest
from key_value.aio.stores.memory import MemoryStore
from mcp.server.auth.provider import AuthorizationParams
from mcp.shared.auth import OAuthClientInformationFull
from pydantic import AnyUrl
from starlette.applications import Starlette
from starlette.testclient import TestClient

from fastmcp.server.auth.auth import AccessToken, TokenVerifier
from fastmcp.server.auth.oauth_proxy import OAuthProxy
from fastmcp.server.auth.oauth_proxy.models import OAuthTransaction


class MockTokenVerifier(TokenVerifier):
    """Mock token verifier for testing."""

    def __init__(self):
        self.required_scopes = ["read", "write"]

    async def verify_token(self, token: str):
        """Mock token verification."""
        return AccessToken(
            token=token,
            client_id="mock-client",
            scopes=self.required_scopes,
            expires_at=int(time.time() + 3600),
        )


class _Verifier(TokenVerifier):
    """Minimal token verifier for security tests."""

    def __init__(self):
        self.required_scopes = ["read"]

    async def verify_token(self, token: str):
        return AccessToken(
            token=token, client_id="c", scopes=self.required_scopes, expires_at=None
        )


@pytest.fixture
def storage():
    """Create a fresh in-memory storage for each test."""
    return MemoryStore()


@pytest.fixture
def oauth_proxy_with_storage(storage):
    """Create OAuth proxy with explicit storage backend."""
    return OAuthProxy(
        upstream_authorization_endpoint="https://github.com/login/oauth/authorize",
        upstream_token_endpoint="https://github.com/login/oauth/access_token",
        upstream_client_id="test-upstream-client",
        upstream_client_secret="test-upstream-secret",
        token_verifier=MockTokenVerifier(),
        base_url="https://myserver.com",
        redirect_path="/auth/callback",
        client_storage=storage,  # Use our test storage
        jwt_signing_key="test-secret",
    )


@pytest.fixture
def oauth_proxy_https():
    """OAuthProxy configured with HTTPS base_url for __Host- cookies."""
    return OAuthProxy(
        upstream_authorization_endpoint="https://github.com/login/oauth/authorize",
        upstream_token_endpoint="https://github.com/login/oauth/access_token",
        upstream_client_id="client-id",
        upstream_client_secret="client-secret",
        token_verifier=_Verifier(),
        base_url="https://myserver.example",
        client_storage=MemoryStore(),
        jwt_signing_key="test-secret",
    )


@pytest.fixture
def oauth_proxy_https_remember():
    """OAuthProxy in 'remember' mode for silent-consent cookie tests."""
    return OAuthProxy(
        upstream_authorization_endpoint="https://github.com/login/oauth/authorize",
        upstream_token_endpoint="https://github.com/login/oauth/access_token",
        upstream_client_id="client-id",
        upstream_client_secret="client-secret",
        token_verifier=_Verifier(),
        base_url="https://myserver.example",
        client_storage=MemoryStore(),
        jwt_signing_key="test-secret",
        require_authorization_consent="remember",
    )


async def _start_flow(
    proxy: OAuthProxy, client_id: str, redirect: str
) -> tuple[str, str]:
    """Register client and start auth; returns (txn_id, consent_url)."""
    await proxy.register_client(
        OAuthClientInformationFull(
            client_id=client_id,
            client_secret="s",
            redirect_uris=[AnyUrl(redirect)],
        )
    )
    params = AuthorizationParams(
        redirect_uri=AnyUrl(redirect),
        redirect_uri_provided_explicitly=True,
        state="client-state-xyz",
        code_challenge="challenge",
        scopes=["read"],
    )
    consent_url = await proxy.authorize(
        OAuthClientInformationFull(
            client_id=client_id,
            client_secret="s",
            redirect_uris=[AnyUrl(redirect)],
        ),
        params,
    )
    qs = parse_qs(urlparse(consent_url).query)
    return qs["txn_id"][0], consent_url


def _extract_csrf(html: str) -> str | None:
    """Extract CSRF token from HTML form."""
    m = re.search(r"name=\"csrf_token\"\s+value=\"([^\"]+)\"", html)
    return m.group(1) if m else None


class TestServerSideStorage:
    """Tests verifying OAuth state is stored in AsyncKeyValue storage."""

    async def test_transaction_stored_in_storage_not_memory(
        self, oauth_proxy_with_storage, storage
    ):
        """Verify OAuth transactions are stored in AsyncKeyValue, not in-memory dict."""
        # Register client
        client = OAuthClientInformationFull(
            client_id="test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:54321/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        # Start authorization flow
        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:54321/callback"),
            redirect_uri_provided_explicitly=True,
            state="client-state-123",
            code_challenge="challenge-abc",
            scopes=["read", "write"],
        )

        redirect_url = await oauth_proxy_with_storage.authorize(client, params)

        # Extract transaction ID from consent redirect
        parsed = urlparse(redirect_url)
        assert "/consent" in parsed.path, "Should redirect to consent page"

        query_params = parse_qs(parsed.query)
        txn_id = query_params["txn_id"][0]

        # Verify transaction is NOT in the old in-memory dict
        # (the attribute should not exist or should be empty)
        assert (
            not hasattr(oauth_proxy_with_storage, "_oauth_transactions")
            or len(getattr(oauth_proxy_with_storage, "_oauth_transactions", {})) == 0
        )

        # Verify transaction IS in storage backend
        transaction = await storage.get(collection="mcp-oauth-transactions", key=txn_id)
        assert transaction is not None, "Transaction should be in storage"

        # Verify transaction has expected structure
        assert transaction["client_id"] == "test-client"
        assert transaction["client_redirect_uri"] == "http://localhost:54321/callback"
        assert transaction["client_state"] == "client-state-123"
        assert transaction["code_challenge"] == "challenge-abc"
        assert transaction["scopes"] == ["read", "write"]

    async def test_authorization_code_stored_in_storage(
        self, oauth_proxy_with_storage, storage
    ):
        """Verify authorization codes are stored in AsyncKeyValue storage."""
        # Register client
        client = OAuthClientInformationFull(
            client_id="test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:54321/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        # Create a test app with OAuth routes
        app = Starlette(routes=oauth_proxy_with_storage.get_routes())

        with TestClient(app) as test_client:
            # Start authorization flow
            params = AuthorizationParams(
                redirect_uri=AnyUrl("http://localhost:54321/callback"),
                redirect_uri_provided_explicitly=True,
                state="client-state",
                code_challenge="challenge-xyz",
                scopes=["read"],
            )

            redirect_url = await oauth_proxy_with_storage.authorize(client, params)

            # Extract txn_id from consent redirect
            parsed = urlparse(redirect_url)
            query_params = parse_qs(parsed.query)
            txn_id = query_params["txn_id"][0]

            # Simulate consent approval
            # First, get the consent page to establish CSRF cookie
            consent_response = test_client.get(
                f"/consent?txn_id={txn_id}", follow_redirects=False
            )

            # Extract CSRF token from response (it's in the HTML form)
            csrf_token = None
            if consent_response.status_code == 200:
                # For this test, we'll generate a CSRF token manually
                # In production, this comes from the consent page HTML
                csrf_token = secrets.token_urlsafe(32)

            # Approve consent with CSRF token
            # Set cookies on client instance to avoid deprecation warning
            for k, v in consent_response.cookies.items():
                test_client.cookies.set(k, v)
            approval_response = test_client.post(
                "/consent",
                data={
                    "action": "approve",
                    "txn_id": txn_id,
                    "csrf_token": csrf_token if csrf_token else "",
                },
                follow_redirects=False,
            )

            # After approval, authorization code should be in storage
            # The code is returned in the redirect URL
            if approval_response.status_code in (302, 303):
                location = approval_response.headers.get("location", "")
                callback_params = parse_qs(urlparse(location).query)

                if "code" in callback_params:
                    auth_code = callback_params["code"][0]

                    # Verify code is NOT in old in-memory dict
                    assert (
                        not hasattr(oauth_proxy_with_storage, "_client_codes")
                        or len(getattr(oauth_proxy_with_storage, "_client_codes", {}))
                        == 0
                    )

                    # Verify code IS in storage
                    code_data = await storage.get(
                        collection="mcp-authorization-codes", key=auth_code
                    )
                    assert code_data is not None, (
                        "Authorization code should be in storage"
                    )
                    assert code_data["client_id"] == "test-client"
                    assert code_data["scopes"] == ["read"]

    async def test_storage_collections_are_isolated(self, oauth_proxy_with_storage):
        """Verify that transactions, codes, and clients use separate collections."""
        # Register a client
        client = OAuthClientInformationFull(
            client_id="isolation-test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:12345/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        # Start authorization to create transaction
        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:12345/callback"),
            redirect_uri_provided_explicitly=True,
            state="test-state",
            code_challenge="test-challenge",
            scopes=["read"],
        )

        await oauth_proxy_with_storage.authorize(client, params)

        # Get all collections from storage
        storage = oauth_proxy_with_storage._client_storage

        # Verify client is in client collection
        client_data = await storage.get(
            collection="mcp-oauth-proxy-clients", key="isolation-test-client"
        )
        assert client_data is not None

        # Verify we can list transactions separately
        # (This tests that collections are properly namespaced)
        transactions = await storage.keys(collection="mcp-oauth-transactions")

        assert len(transactions) > 0, "Should have at least one transaction"

        # Verify transaction keys don't collide with client keys
        for txn_key in transactions:
            assert txn_key != "isolation-test-client"


class TestConsentFlowRedirects:
    """Tests for consent flow redirect behavior."""

    async def test_authorize_redirects_to_consent_page(self, oauth_proxy_with_storage):
        """Verify authorize() redirects to /consent instead of upstream."""
        client = OAuthClientInformationFull(
            client_id="consent-test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:8080/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:8080/callback"),
            redirect_uri_provided_explicitly=True,
            state="test-state",
            code_challenge="",
            scopes=["read"],
        )

        redirect_url = await oauth_proxy_with_storage.authorize(client, params)

        # Should redirect to consent page, not upstream
        assert "/consent" in redirect_url
        assert "github.com" not in redirect_url
        assert "?txn_id=" in redirect_url

    async def test_consent_page_contains_transaction_id(self, oauth_proxy_with_storage):
        """Verify consent page receives and displays transaction ID."""
        client = OAuthClientInformationFull(
            client_id="txn-test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:9090/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:9090/callback"),
            redirect_uri_provided_explicitly=True,
            state="test-state",
            code_challenge="test-challenge",
            scopes=["read", "write"],
        )

        redirect_url = await oauth_proxy_with_storage.authorize(client, params)

        # Extract txn_id parameter
        parsed = urlparse(redirect_url)
        query = parse_qs(parsed.query)

        assert "txn_id" in query
        txn_id = query["txn_id"][0]
        assert len(txn_id) > 0

        # Create test client
        app = Starlette(routes=oauth_proxy_with_storage.get_routes())

        with TestClient(app) as test_client:
            # Request consent page
            response = test_client.get(
                f"/consent?txn_id={txn_id}", follow_redirects=False
            )

            assert response.status_code == 200
            # Consent page should contain transaction reference
            assert txn_id.encode() in response.content or b"consent" in response.content


class TestCSRFProtection:
    """Tests for CSRF protection in consent flow."""

    async def test_consent_requires_csrf_token(self, oauth_proxy_with_storage):
        """Verify consent submission requires valid CSRF token."""
        client = OAuthClientInformationFull(
            client_id="csrf-test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:7070/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:7070/callback"),
            redirect_uri_provided_explicitly=True,
            state="test-state",
            code_challenge="",
            scopes=["read"],
        )

        redirect_url = await oauth_proxy_with_storage.authorize(client, params)
        parsed = urlparse(redirect_url)
        query = parse_qs(parsed.query)
        txn_id = query["txn_id"][0]

        app = Starlette(routes=oauth_proxy_with_storage.get_routes())

        with TestClient(app) as test_client:
            # Try to submit consent WITHOUT CSRF token
            response = test_client.post(
                "/consent",
                data={"action": "approve", "txn_id": txn_id},
                # No CSRF token!
                follow_redirects=False,
            )

            # Should reject or require CSRF
            # (Implementation may vary - checking for error response)
            assert response.status_code in (
                400,
                403,
                302,
            )  # Error or redirect to error

    async def test_consent_cookie_established_on_page_visit(
        self, oauth_proxy_with_storage
    ):
        """Verify consent page establishes CSRF cookie."""
        client = OAuthClientInformationFull(
            client_id="cookie-test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:6060/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:6060/callback"),
            redirect_uri_provided_explicitly=True,
            state="test-state",
            code_challenge="",
            scopes=["read"],
        )

        redirect_url = await oauth_proxy_with_storage.authorize(client, params)
        parsed = urlparse(redirect_url)
        query = parse_qs(parsed.query)
        txn_id = query["txn_id"][0]

        app = Starlette(routes=oauth_proxy_with_storage.get_routes())

        with TestClient(app) as test_client:
            # Visit consent page
            response = test_client.get(
                f"/consent?txn_id={txn_id}", follow_redirects=False
            )

            # Should set cookies for CSRF protection
            assert response.status_code == 200
            # Cookie may be set via Set-Cookie header
            cookies = response.cookies
            # Look for any CSRF-related cookie (implementation dependent)
            assert len(cookies) > 0 or "csrf" in response.text.lower(), (
                "Consent page should establish CSRF protection"
            )


class TestCSRFDoubleSubmit:
    """Tests for CSRF double-submit cookie validation (GHSA-rww4-4w9c-7733 bypass)."""

    async def test_consent_rejected_without_csrf_cookie(self, oauth_proxy_with_storage):
        """Submitting a valid CSRF token without the matching cookie should be rejected.

        This prevents an attacker from using their own tx_id/csrf_token to CSRF
        the victim's browser into approving consent.
        """
        txn_id, _ = await _start_flow(
            oauth_proxy_with_storage,
            "csrf-double-submit-client",
            "http://localhost:9090/callback",
        )

        app = Starlette(routes=oauth_proxy_with_storage.get_routes())
        with TestClient(app) as test_client:
            # Visit consent page to populate the transaction with a CSRF token
            consent_resp = test_client.get(f"/consent?txn_id={txn_id}")
            assert consent_resp.status_code == 200
            csrf_token = _extract_csrf(consent_resp.text)
            assert csrf_token

        # Simulate the attack: use a FRESH client (no cookies from the consent
        # page) to submit the form with a valid CSRF token — as if the attacker
        # tricked the victim's browser into POSTing their tx_id/csrf_token.
        with TestClient(app) as attacker_client:
            response = attacker_client.post(
                "/consent",
                data={
                    "action": "approve",
                    "txn_id": txn_id,
                    "csrf_token": csrf_token,
                },
                follow_redirects=False,
            )
            assert response.status_code == 403


class TestStoragePersistence:
    """Tests for state persistence across storage backends."""

    async def test_transaction_persists_after_retrieval(self, oauth_proxy_with_storage):
        """Verify transaction can be retrieved multiple times (until deleted)."""
        client = OAuthClientInformationFull(
            client_id="persist-test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:5050/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:5050/callback"),
            redirect_uri_provided_explicitly=True,
            state="persist-state",
            code_challenge="persist-challenge",
            scopes=["read"],
        )

        redirect_url = await oauth_proxy_with_storage.authorize(client, params)
        parsed = urlparse(redirect_url)
        query = parse_qs(parsed.query)
        txn_id = query["txn_id"][0]

        storage = oauth_proxy_with_storage._client_storage

        # Retrieve transaction multiple times
        txn1 = await storage.get(collection="mcp-oauth-transactions", key=txn_id)
        assert txn1 is not None

        txn2 = await storage.get(collection="mcp-oauth-transactions", key=txn_id)
        assert txn2 is not None

        # Should be the same data
        assert txn1["client_id"] == txn2["client_id"]
        assert txn1["client_state"] == txn2["client_state"]

    async def test_storage_uses_pydantic_adapter(self, oauth_proxy_with_storage):
        """Verify that PydanticAdapter serializes/deserializes correctly."""
        client = OAuthClientInformationFull(
            client_id="pydantic-test-client",
            client_secret="test-secret",
            redirect_uris=[AnyUrl("http://localhost:4040/callback")],
        )
        await oauth_proxy_with_storage.register_client(client)

        params = AuthorizationParams(
            redirect_uri=AnyUrl("http://localhost:4040/callback"),
            redirect_uri_provided_explicitly=True,
            state="pydantic-state",
            code_challenge="pydantic-challenge",
            scopes=["read", "write"],
        )

        redirect_url = await oauth_proxy_with_storage.authorize(client, params)
        parsed = urlparse(redirect_url)
        query = parse_qs(parsed.query)
        txn_id = query["txn_id"][0]

        # Retrieve using PydanticAdapter (which is what the proxy uses)
        transaction_store = oauth_proxy_with_storage._transaction_store
        txn_model = await transaction_store.get(key=txn_id)

        # Should be a Pydantic model instance
        assert isinstance(txn_model, OAuthTransaction)
        assert txn_model.client_id == "pydantic-test-client"
        assert txn_model.client_state == "pydantic-state"
        assert txn_model.code_challenge == "pydantic-challenge"
        assert txn_model.scopes == ["read", "write"]


class TestConsentSecurity:
    """Tests for consent page security features."""

    async def test_consent_sets_xfo_header(self, oauth_proxy_https):
        """Verify consent page sets X-Frame-Options header to prevent clickjacking."""
        txn_id, _ = await _start_flow(
            oauth_proxy_https, "client-a", "http://localhost:5001/callback"
        )
        app = Starlette(routes=oauth_proxy_https.get_routes())
        with TestClient(app) as c:
            r = c.get(f"/consent?txn_id={txn_id}")
            assert r.status_code == 200
            assert r.headers.get("X-Frame-Options") == "DENY"

    async def test_deny_sets_cookie_and_redirects_with_error(
        self, oauth_proxy_https_remember
    ):
        """Verify denying consent in 'remember' mode sets signed cookie and redirects with error."""
        client_redirect = "http://localhost:5002/callback"
        txn_id, _ = await _start_flow(
            oauth_proxy_https_remember, "client-b", client_redirect
        )
        app = Starlette(routes=oauth_proxy_https_remember.get_routes())
        with TestClient(app) as c:
            consent = c.get(f"/consent?txn_id={txn_id}")
            csrf = _extract_csrf(consent.text)
            assert csrf
            # Persist consent page cookies on client instance to avoid per-request deprecation
            for k, v in consent.cookies.items():
                c.cookies.set(k, v)
            r = c.post(
                "/consent",
                data={"action": "deny", "txn_id": txn_id, "csrf_token": csrf},
                follow_redirects=False,
            )
            assert r.status_code in (302, 303)
            loc = r.headers.get("location", "")
            parsed = urlparse(loc)
            assert parsed.scheme == "http" and parsed.netloc.startswith("localhost")
            q = parse_qs(parsed.query)
            assert q.get("error") == ["access_denied"]
            assert q.get("state") == ["client-state-xyz"]
            # Signed denied cookie should be set
            assert "MCP_DENIED_CLIENTS" in ";\n".join(
                r.headers.get("set-cookie", "").splitlines()
            )

    async def test_approve_sets_cookie_and_redirects_to_upstream(
        self, oauth_proxy_https_remember
    ):
        """Verify approving consent in 'remember' mode sets signed cookie and redirects to upstream."""
        txn_id, _ = await _start_flow(
            oauth_proxy_https_remember, "client-c", "http://localhost:5003/callback"
        )
        app = Starlette(routes=oauth_proxy_https_remember.get_routes())
        with TestClient(app) as c:
            consent = c.get(f"/consent?txn_id={txn_id}")
            csrf = _extract_csrf(consent.text)
            assert csrf
            for k, v in consent.cookies.items():
                c.cookies.set(k, v)
            r = c.post(
                "/consent",
                data={"action": "approve", "txn_id": txn_id, "csrf_token": csrf},
                follow_redirects=False,
            )
            assert r.status_code in (302, 303)
            loc = r.headers.get("location", "")
            assert loc.startswith("https://github.com/login/oauth/authorize")
            assert f"state={txn_id}" in loc
            # Signed approved cookie should be set with __Host- prefix for HTTPS
            set_cookie = ";\n".join(r.headers.get("set-cookie", "").splitlines())
            assert "__Host-MCP_APPROVED_CLIENTS" in set_cookie

    async def test_tampered_cookie_is_ignored(self, oauth_proxy_https_remember):
        """Verify tampered approval cookie is ignored and consent page shown."""
        txn_id, _ = await _start_flow(
            oauth_proxy_https_remember, "client-d", "http://localhost:5004/callback"
        )
        app = Starlette(routes=oauth_proxy_https_remember.get_routes())
        with TestClient(app) as c:
            # Create a tampered cookie (invalid signature)
            # Value format: payload.signature; using wrong signature to force failure
            tampered_value = "W10=.invalidsig"
            c.cookies.set("__Host-MCP_APPROVED_CLIENTS", tampered_value)
            r = c.get(
                f"/consent?txn_id={txn_id}",
                headers={"Sec-Fetch-Site": "none"},
                follow_redirects=False,
            )
            # Should not auto-redirect to upstream; should show consent page
            assert r.status_code == 200
            # httpx returns a URL object; compare path or stringify
            assert urlparse(str(r.request.url)).path == "/consent"

    async def test_autoapprove_cookie_skips_consent(self, oauth_proxy_https_remember):
        """Verify valid approval cookie auto-approves and redirects to upstream in 'remember' mode."""
        client_id = "client-e"
        redirect = "http://localhost:5005/callback"
        txn_id, _ = await _start_flow(oauth_proxy_https_remember, client_id, redirect)
        app = Starlette(routes=oauth_proxy_https_remember.get_routes())
        with TestClient(app) as c:
            # Approve once to set approved cookie
            consent = c.get(f"/consent?txn_id={txn_id}")
            csrf = _extract_csrf(consent.text)
            for k, v in consent.cookies.items():
                c.cookies.set(k, v)
            r = c.post(
                "/consent",
                data={
                    "action": "approve",
                    "txn_id": txn_id,
                    "csrf_token": csrf if csrf else "",
                },
                follow_redirects=False,
            )
            # Extract approved cookie value
            set_cookie = ";\n".join(r.headers.get("set-cookie", "").splitlines())
            m = re.search(r"__Host-MCP_APPROVED_CLIENTS=([^;]+)", set_cookie)
            assert m, "approved cookie should be set in 'remember' mode"
            approved_cookie = m.group(1)

            # Start a new flow for the same client and redirect
            new_txn, _ = await _start_flow(
                oauth_proxy_https_remember, client_id, redirect
            )
            # Should auto-redirect to upstream when visiting consent due to cookie
            # (requires a safe Sec-Fetch-Site value — "none" simulates a direct
            # client-initiated navigation like an MCP host opening the browser).
            c.cookies.set("__Host-MCP_APPROVED_CLIENTS", approved_cookie)
            r2 = c.get(
                f"/consent?txn_id={new_txn}",
                headers={"Sec-Fetch-Site": "none"},
                follow_redirects=False,
            )
            assert r2.status_code in (302, 303)
            assert r2.headers.get("location", "").startswith(
                "https://github.com/login/oauth/authorize"
            )


class TestConsentModes:
    """Tests for the three consent modes: True (always), 'remember' (silent), 'external'.

    Covers the default behavior where True no longer silently approves return
    visits, and 'remember' mode gates silent consent on Sec-Fetch-Site to
    block AS-in-the-middle attacks.
    """

    async def test_default_mode_does_not_set_approval_cookie(self, oauth_proxy_https):
        """Approving in default (True) mode must NOT set a long-lived approval cookie.

        In 'always prompt' mode there's no reason to remember approvals, and
        writing the cookie would only create a no-op attack surface.
        """
        txn_id, _ = await _start_flow(
            oauth_proxy_https, "client-default", "http://localhost:7001/callback"
        )
        app = Starlette(routes=oauth_proxy_https.get_routes())
        with TestClient(app) as c:
            consent = c.get(f"/consent?txn_id={txn_id}")
            csrf = _extract_csrf(consent.text)
            assert csrf
            for k, v in consent.cookies.items():
                c.cookies.set(k, v)
            r = c.post(
                "/consent",
                data={"action": "approve", "txn_id": txn_id, "csrf_token": csrf},
                follow_redirects=False,
            )
            assert r.status_code in (302, 303)
            set_cookie = ";\n".join(r.headers.get("set-cookie", "").splitlines())
            # Consent binding cookie still set for the in-flight transaction
            assert "__Host-MCP_CONSENT_BINDING" in set_cookie
            # But no remembered-approval cookie
            assert "MCP_APPROVED_CLIENTS" not in set_cookie

    async def test_default_mode_ignores_existing_approval_cookie(
        self, oauth_proxy_https_remember, oauth_proxy_https
    ):
        """A valid approval cookie is ignored in default (True) mode — always prompts.

        Uses the 'remember' proxy to generate a legitimately-signed cookie, then
        replays it against a default-mode proxy (same jwt_signing_key) to confirm
        the consent page is still shown.
        """
        # Both fixtures use the same signing key, so cookies generated by one
        # verify against the other.
        client_id = "client-xmode"
        redirect = "http://localhost:7002/callback"
        txn_id, _ = await _start_flow(oauth_proxy_https_remember, client_id, redirect)
        app_remember = Starlette(routes=oauth_proxy_https_remember.get_routes())
        with TestClient(app_remember) as c:
            consent = c.get(f"/consent?txn_id={txn_id}")
            csrf = _extract_csrf(consent.text)
            assert csrf
            for k, v in consent.cookies.items():
                c.cookies.set(k, v)
            r = c.post(
                "/consent",
                data={"action": "approve", "txn_id": txn_id, "csrf_token": csrf},
                follow_redirects=False,
            )
            set_cookie_remember = ";\n".join(
                r.headers.get("set-cookie", "").splitlines()
            )
            m = re.search(r"__Host-MCP_APPROVED_CLIENTS=([^;]+)", set_cookie_remember)
            assert m, "remember-mode proxy should have set approval cookie"
            approved_cookie = m.group(1)

        # Now replay against the default-mode proxy for the same client/redirect.
        new_txn, _ = await _start_flow(oauth_proxy_https, client_id, redirect)
        app_default = Starlette(routes=oauth_proxy_https.get_routes())
        with TestClient(app_default) as c:
            c.cookies.set("__Host-MCP_APPROVED_CLIENTS", approved_cookie)
            r = c.get(
                f"/consent?txn_id={new_txn}",
                headers={"Sec-Fetch-Site": "none"},
                follow_redirects=False,
            )
            # Default mode: HTML consent page, no silent redirect to upstream.
            assert r.status_code == 200
            assert "text/html" in r.headers.get("content-type", "")

    async def test_remember_mode_cross_site_forces_prompt(
        self, oauth_proxy_https_remember
    ):
        """Sec-Fetch-Site=cross-site must skip silent consent even with valid cookie.

        Blocks the AS-in-the-middle scenario: attacker redirects the victim's
        browser to /authorize from a third-party origin, which browsers mark
        cross-site. Legit local-host flows are Sec-Fetch-Site=none.
        """
        client_id = "client-cross"
        redirect = "http://localhost:7003/callback"
        txn_id, _ = await _start_flow(oauth_proxy_https_remember, client_id, redirect)
        app = Starlette(routes=oauth_proxy_https_remember.get_routes())
        with TestClient(app) as c:
            # Seed a valid approval cookie via the normal consent flow.
            consent = c.get(f"/consent?txn_id={txn_id}")
            csrf = _extract_csrf(consent.text)
            assert csrf
            for k, v in consent.cookies.items():
                c.cookies.set(k, v)
            r = c.post(
                "/consent",
                data={"action": "approve", "txn_id": txn_id, "csrf_token": csrf},
                follow_redirects=False,
            )
            set_cookie = ";\n".join(r.headers.get("set-cookie", "").splitlines())
            m = re.search(r"__Host-MCP_APPROVED_CLIENTS=([^;]+)", set_cookie)
            assert m
            approved_cookie = m.group(1)

            # Start a new flow and simulate a cross-site navigation.
            new_txn, _ = await _start_flow(
                oauth_proxy_https_remember, client_id, redirect
            )
            c.cookies.set("__Host-MCP_APPROVED_CLIENTS", approved_cookie)
            r2 = c.get(
                f"/consent?txn_id={new_txn}",
                headers={"Sec-Fetch-Site": "cross-site"},
                follow_redirects=False,
            )
            # Silent consent skipped; HTML prompt shown.
            assert r2.status_code == 200
            assert "text/html" in r2.headers.get("content-type", "")

    async def test_remember_mode_missing_sec_fetch_site_fails_closed(
        self, oauth_proxy_https_remember
    ):
        """Missing Sec-Fetch-Site header must fall back to the explicit prompt.

        Legacy clients that don't send the header degrade to the safer behavior
        rather than granting silent consent.
        """
        client_id = "client-nofetch"
        redirect = "http://localhost:7004/callback"
        txn_id, _ = await _start_flow(oauth_proxy_https_remember, client_id, redirect)
        app = Starlette(routes=oauth_proxy_https_remember.get_routes())
        with TestClient(app) as c:
            consent = c.get(f"/consent?txn_id={txn_id}")
            csrf = _extract_csrf(consent.text)
            assert csrf
            for k, v in consent.cookies.items():
                c.cookies.set(k, v)
            r = c.post(
                "/consent",
                data={"action": "approve", "txn_id": txn_id, "csrf_token": csrf},
                follow_redirects=False,
            )
            set_cookie = ";\n".join(r.headers.get("set-cookie", "").splitlines())
            m = re.search(r"__Host-MCP_APPROVED_CLIENTS=([^;]+)", set_cookie)
            assert m
            approved_cookie = m.group(1)

            new_txn, _ = await _start_flow(
                oauth_proxy_https_remember, client_id, redirect
            )
            c.cookies.set("__Host-MCP_APPROVED_CLIENTS", approved_cookie)
            # No Sec-Fetch-Site header at all.
            r2 = c.get(f"/consent?txn_id={new_txn}", follow_redirects=False)
            assert r2.status_code == 200
            assert "text/html" in r2.headers.get("content-type", "")