diff --git a/packages/oauth/src/keycardai/oauth/pkce/__init__.py b/packages/oauth/src/keycardai/oauth/pkce/__init__.py
index e83a443..a13f07c 100644
--- a/packages/oauth/src/keycardai/oauth/pkce/__init__.py
+++ b/packages/oauth/src/keycardai/oauth/pkce/__init__.py
@@ -31,10 +31,12 @@
         client_id="my-app",
         issuer="https://auth.example.com",
         redirect_uri="https://app.example.com/oauth/callback",
+        resources=["https://api.example.com", "https://files.example.com"],
     )
     session["oauth_flow"] = {
         "state": redirect.state,
         "code_verifier": redirect.code_verifier,
+        "resources": redirect.resources,
     }
     # Redirect the browser to ``redirect.url``. In the callback route:
     flow = session.pop("oauth_flow")
diff --git a/packages/oauth/src/keycardai/oauth/pkce/web.py b/packages/oauth/src/keycardai/oauth/pkce/web.py
index 3fd6c3d..7cd0657 100644
--- a/packages/oauth/src/keycardai/oauth/pkce/web.py
+++ b/packages/oauth/src/keycardai/oauth/pkce/web.py
@@ -27,7 +27,7 @@
     TokenResponse,
 )
 from ..utils.pkce import PKCEGenerator
-from ._issuer import _resolve_auth_server_url
+from ._issuer import resolve_issuer_from_challenge
 
 
 class AuthorizationRedirect(BaseModel):
@@ -38,18 +38,25 @@ class AuthorizationRedirect(BaseModel):
         state: The generated CSRF value to store until the callback.
         code_verifier: The PKCE verifier to store until the callback. This
             value must never be sent to the browser.
+        resources: The resources the authorization request was scoped to,
+            carried so the application can persist them alongside ``state``
+            and ``code_verifier``. They are not needed to redeem the code —
+            the authorization server derives the issued token's audience from
+            the code itself — but applications commonly need to know which
+            resources a session was authorized for.
     """
 
     url: str
     state: str
     code_verifier: str
+    resources: list[str] | None = None
 
 
 async def begin_authorization(
     *,
     client_id: str,
     redirect_uri: str,
-    resource_url: str | None = None,
+    resources: list[str] | None = None,
     www_authenticate_header: str | None = None,
     issuer: str | None = None,
     metadata: AuthorizationServerMetadata | None = None,
@@ -65,8 +72,10 @@ async def begin_authorization(
     Args:
         client_id: OAuth client ID.
         redirect_uri: Registered redirect URI handled by the web application.
-        resource_url: The protected resource the caller is targeting. Passed
-            as the RFC 8707 ``resource`` parameter when provided.
+        resources: The protected resources the caller is targeting. Each entry
+            is sent as its own RFC 8707 ``resource`` query parameter, so a
+            single authorization can cover several resources and the issued
+            token's audience covers all of them.
         www_authenticate_header: The ``WWW-Authenticate`` challenge from the
             protected resource. Must contain a ``resource_metadata`` URL per
             RFC 9728. Mutually exclusive with ``issuer``.
@@ -82,16 +91,16 @@ async def begin_authorization(
 
     Returns:
         ``AuthorizationRedirect`` containing the authorization URL, generated
-        state, and PKCE code verifier. Store the state and verifier in
-        application-controlled session state.
+        state, PKCE code verifier, and the requested resources. Store the
+        state and verifier in application-controlled session state.
 
     Raises:
         keycardai.oauth.ConfigError: If anything other than exactly one of
             ``issuer``, ``www_authenticate_header``, or ``metadata`` is
-            provided, or challenge mode omits ``resource_url``.
-        ValueError: If the authorization endpoint is missing from the supplied
-            metadata or discovered server metadata, or if challenge discovery
-            metadata is incomplete.
+            provided, or challenge mode omits ``resources``.
+        ValueError: If the authorization endpoint is missing from the
+            supplied metadata or discovered server metadata, or if challenge
+            discovery metadata is incomplete.
         httpx.HTTPStatusError: If fetching protected resource metadata fails.
         keycardai.oauth.OAuthHttpError: If authorization server discovery
             returns an HTTP error.
@@ -111,10 +120,14 @@ async def begin_authorization(
             )
         authorization_endpoint = metadata.authorization_endpoint
     else:
-        auth_server_url = await _resolve_auth_server_url(
+        if www_authenticate_header is not None and not resources:
+            raise ConfigError(
+                "'resources' is required when authenticating from a "
+                "WWW-Authenticate challenge"
+            )
+        auth_server_url = await _resolve_issuer(
             issuer=issuer,
             www_authenticate_header=www_authenticate_header,
-            resource_url=resource_url,
             http_client=http_client,
         )
         config = ClientConfig(
@@ -138,7 +151,7 @@ async def begin_authorization(
         client_id=client_id,
         redirect_uri=redirect_uri,
         pkce=pkce,
-        resources=[resource_url] if resource_url else None,
+        resources=resources,
         scope=" ".join(scopes) if scopes else None,
         state=state,
     )
@@ -147,6 +160,7 @@ async def begin_authorization(
         url=url,
         state=state,
         code_verifier=pkce.code_verifier,
+        resources=resources,
     )
 
 
@@ -157,7 +171,6 @@ async def complete_authorization(
     code_verifier: str,
     client_id: str,
     redirect_uri: str,
-    resource_url: str | None = None,
     www_authenticate_header: str | None = None,
     issuer: str | None = None,
     metadata: AuthorizationServerMetadata | None = None,
@@ -170,6 +183,11 @@ async def complete_authorization(
     The application supplies the ``state`` and ``code_verifier`` retained
     from :func:`begin_authorization`.
 
+    No RFC 8707 ``resource`` parameter is sent on the token request: the
+    authorization server derives the issued token's audience from the
+    authorization code, which already records the resources the user
+    authorized in the begin step.
+
     Args:
         callback_params: Query parameters received by the application's
             callback route, including ``code`` and ``state`` or an OAuth
@@ -179,8 +197,6 @@ async def complete_authorization(
             value must never be sent to the browser.
         client_id: OAuth client ID.
         redirect_uri: The same registered redirect URI used in the begin step.
-        resource_url: The protected resource the caller is targeting. Passed
-            as the RFC 8707 ``resource`` parameter when provided.
         www_authenticate_header: The ``WWW-Authenticate`` challenge from the
             protected resource. Must contain a ``resource_metadata`` URL per
             RFC 9728. Mutually exclusive with ``issuer``.
@@ -202,7 +218,7 @@ async def complete_authorization(
     Raises:
         keycardai.oauth.ConfigError: If anything other than exactly one of
             ``issuer``, ``www_authenticate_header``, or ``metadata`` is
-            provided, or challenge mode omits ``resource_url``.
+            provided.
         ValueError: If the token endpoint is missing from the supplied
             metadata or discovered server metadata, or if challenge discovery
             metadata is incomplete.
@@ -250,10 +266,9 @@ async def complete_authorization(
             )
         auth_server_url = metadata.issuer
     else:
-        auth_server_url = await _resolve_auth_server_url(
+        auth_server_url = await _resolve_issuer(
             issuer=issuer,
             www_authenticate_header=www_authenticate_header,
-            resource_url=resource_url,
             http_client=http_client,
         )
 
@@ -281,10 +296,28 @@ async def complete_authorization(
             redirect_uri=redirect_uri,
             code_verifier=code_verifier,
             client_id=client_id,
-            resource=resource_url,
         )
 
 
+
+async def _resolve_issuer(
+    *,
+    issuer: str | None,
+    www_authenticate_header: str | None,
+    http_client: httpx.AsyncClient | None,
+) -> str:
+    if issuer is not None:
+        return issuer.rstrip("/")
+    if www_authenticate_header is None:
+        raise ConfigError(
+            "Provide exactly one of 'issuer', 'www_authenticate_header', "
+            "or 'metadata'"
+        )
+    return await resolve_issuer_from_challenge(
+        www_authenticate_header, http_client=http_client
+    )
+
+
 def _validate_entry_mode(
     *,
     issuer: str | None,
diff --git a/packages/oauth/tests/keycardai/oauth/pkce/test_web.py b/packages/oauth/tests/keycardai/oauth/pkce/test_web.py
index 5a2b8aa..8eeab69 100644
--- a/packages/oauth/tests/keycardai/oauth/pkce/test_web.py
+++ b/packages/oauth/tests/keycardai/oauth/pkce/test_web.py
@@ -44,12 +44,16 @@ async def test_begin_returns_redirect_and_pkce_values(monkeypatch):
         issuer="https://auth.example.com",
         redirect_uri="https://app.example.com/callback",
         scopes=["openid", "profile"],
-        resource_url="https://api.example.com",
+        resources=["https://api.example.com", "https://files.example.com"],
     )
 
     assert isinstance(result, AuthorizationRedirect)
     assert result.state
     assert result.code_verifier
+    assert result.resources == [
+        "https://api.example.com",
+        "https://files.example.com",
+    ]
     params = parse_qs(urlsplit(result.url).query)
     assert params["state"] == [result.state]
     assert params["code_challenge"] == [
@@ -57,10 +61,41 @@ async def test_begin_returns_redirect_and_pkce_values(monkeypatch):
     ]
     assert params["code_challenge_method"] == ["S256"]
     assert params["scope"] == ["openid profile"]
-    assert params["resource"] == ["https://api.example.com"]
+    assert params["resource"] == [
+        "https://api.example.com",
+        "https://files.example.com",
+    ]
     assert captured["issuer"] == "https://auth.example.com"
 
 
+@pytest.mark.asyncio
+async def test_begin_rejects_removed_resource_url():
+    with pytest.raises(TypeError, match="resource_url"):
+        await begin_authorization(
+            client_id="my-app",
+            issuer="https://auth.example.com",
+            redirect_uri="https://app.example.com/callback",
+            resource_url="https://api.example.com",
+        )
+
+
+@pytest.mark.asyncio
+async def test_begin_without_resources_sends_no_resource_parameter(monkeypatch):
+    monkeypatch.setattr(
+        "keycardai.oauth.pkce.web.AsyncClient",
+        _async_client_factory(),
+    )
+
+    result = await begin_authorization(
+        client_id="my-app",
+        issuer="https://auth.example.com",
+        redirect_uri="https://app.example.com/callback",
+    )
+
+    assert result.resources is None
+    assert "resource" not in parse_qs(urlsplit(result.url).query)
+
+
 @pytest.mark.asyncio
 async def test_begin_uses_metadata_without_constructing_client(monkeypatch):
     async_client = MagicMock()
@@ -100,7 +135,6 @@ async def test_complete_exchanges_matching_state(monkeypatch):
         client_id="my-app",
         issuer="https://auth.example.com",
         redirect_uri="https://app.example.com/callback",
-        resource_url="https://api.example.com",
     )
 
     assert result is token
@@ -109,10 +143,23 @@ async def test_complete_exchanges_matching_state(monkeypatch):
         "redirect_uri": "https://app.example.com/callback",
         "code_verifier": "stored-verifier",
         "client_id": "my-app",
-        "resource": "https://api.example.com",
     }
 
 
+@pytest.mark.asyncio
+async def test_complete_rejects_removed_resource_url():
+    with pytest.raises(TypeError, match="resource_url"):
+        await complete_authorization(
+            callback_params={"code": "auth-code", "state": "stored-state"},
+            state="stored-state",
+            code_verifier="stored-verifier",
+            client_id="my-app",
+            issuer="https://auth.example.com",
+            redirect_uri="https://app.example.com/callback",
+            resource_url="https://api.example.com",
+        )
+
+
 @pytest.mark.asyncio
 async def test_complete_uses_metadata_without_discovery(monkeypatch):
     captured = {}
@@ -299,7 +346,7 @@ async def test_begin_resolves_issuer_from_challenge(monkeypatch):
     await begin_authorization(
         client_id="my-app",
         redirect_uri="https://app.example.com/callback",
-        resource_url="https://api.example.com",
+        resources=["https://api.example.com"],
         www_authenticate_header=WWW_AUTHENTICATE,
         http_client=http_client,
     )
@@ -346,8 +393,8 @@ async def test_flow_requires_exactly_one_issuer_entry(function, kwargs):
 
 
 @pytest.mark.asyncio
-async def test_begin_challenge_mode_requires_resource_url():
-    with pytest.raises(ConfigError, match="resource_url"):
+async def test_begin_challenge_mode_requires_resources():
+    with pytest.raises(ConfigError, match="resources"):
         await begin_authorization(
             client_id="my-app",
             redirect_uri="https://app.example.com/callback",