Support multiple OIDC providers

kaya-oidc 0.0.6 can run several providers in one app (OIDCProviders),
each with its own login route and namespaced session state. Adopt it:
providers are configured in indexed, contiguous OIDC_<n>_* blocks
(0-based) with OIDC_<n>_PROVIDER naming the provider in its login URL
and session keys. The old unindexed OIDC_ISSUER/OIDC_CLIENT_ID/... names
are no longer read; startup fails with a rename hint when they are set.
With no OIDC variables at all, the single dev mock provider named
"default" is used, as before.

The platform now authenticates through OIDCProviders: auth.current_user
returns the session's user (sessions stay single-identity, so at most one
provider is logged in) and require_auth/route handlers use it, while the
websocket path keeps scanning for any provider's user. New routes expose
the configuration to the SPA and keep old links working: GET
/api/auth/providers lists the login URLs, GET /auth/login redirects to
the first provider and GET /auth/logout to whichever provider the
session is logged in with. The lobby renders one login button per
provider from that endpoint.

Update the env examples, compose and k8s manifests to the indexed scheme,
document the multiple-provider setup and the migration, and cover it with
config, auth and route tests.

server/packages/tavolo-platform/tests/test_auth.py

@@ -1,9 +1,9 @@
-"""Tests for the auth helpers' OIDC user lookup.
+"""Tests for the auth helpers' OIDC user lookup and gating.
 
 kaya-oidc (0.0.6) namespaces session state per provider as
-``oidc:{provider}:user``; these tests pin that contract so a kaya
-upgrade that changes it again cannot silently break websocket
-authentication or span tagging.
+``oidc:{provider}:user`` and tavolo wires an :class:`OIDCProviders`; these
+tests pin both contracts so a kaya upgrade or a provider change cannot
+silently break HTTP or websocket authentication.
 """
 from __future__ import annotations
 
@@ -11,9 +11,31 @@ import unittest
 from types import SimpleNamespace
 from typing import Any
 
-from kaya.session import Session
+from kaya.oidc import OIDCConfig, OIDCProviders
+from kaya.session import InMemorySessionStore, Session, SessionMixin
 
-from tavolo.platform.auth import get_ws_user, session_user
+from helpers import async_test
+from tavolo.platform.auth import current_user, get_ws_user, require_auth, session_user
+
+
+def _providers(*names: str) -> OIDCProviders:
+    session = SessionMixin(InMemorySessionStore())
+    return OIDCProviders(
+        [
+            OIDCConfig(
+                provider=name,
+                issuer=f"http://localhost:8180/{name}",
+                client_id="tavolo",
+                redirect_uri=f"http://localhost:8080/auth/{name}/callback",
+            )
+            for name in names
+        ],
+        session=session,
+    )
+
+
+def _ctx(data: Any) -> Any:
+    return SimpleNamespace(session=Session("sid", data))
 
 
 def _ws(session: Any) -> Any:
@@ -63,3 +85,68 @@ class GetWsUserTest(unittest.TestCase):
 
     def test_missing_session_returns_none(self) -> None:
         self.assertIsNone(get_ws_user(SimpleNamespace()))
+
+
+class CurrentUserTest(unittest.TestCase):
+    def test_anonymous_session_has_no_user(self) -> None:
+        self.assertIsNone(current_user(_providers("default"), _ctx({})))
+
+    def test_returns_the_authenticated_provider_user(self) -> None:
+        user = current_user(
+            _providers("default", "google"),
+            _ctx({"oidc:google:user": {"sub": "alice"}}),
+        )
+        assert user is not None
+        self.assertEqual("alice", user.sub)
+
+    def test_first_configured_provider_wins(self) -> None:
+        # Single-identity sessions never hold two users; this only pins the
+        # tie-break should they ever coexist.
+        user = current_user(
+            _providers("default", "google"),
+            _ctx(
+                {
+                    "oidc:default:user": {"sub": "alice"},
+                    "oidc:google:user": {"sub": "bob"},
+                }
+            ),
+        )
+        assert user is not None
+        self.assertEqual("alice", user.sub)
+
+
+class RequireAuthTest(unittest.TestCase):
+    @async_test
+    async def test_rejects_anonymous_requests(self) -> None:
+        oidc = _providers("default")
+        ctx = _ctx({})
+        sent = {}
+
+        async def send_bytes(*args: Any) -> None:
+            sent["status"] = args[0]
+
+        ctx.send_bytes = send_bytes
+        handled = []
+
+        @require_auth(oidc)
+        async def handler(_ctx: Any) -> None:
+            handled.append(True)
+
+        await handler(ctx)
+        self.assertEqual(401, sent["status"])
+        self.assertEqual([], handled)
+
+    @async_test
+    async def test_allows_authenticated_requests(self) -> None:
+        oidc = _providers("default")
+        ctx = _ctx({"oidc:default:user": {"sub": "alice"}})
+        handled = []
+
+        @require_auth(oidc)
+        async def handler(request_ctx: Any) -> None:
+            user = current_user(oidc, request_ctx)
+            assert user is not None
+            handled.append(user.sub)
+
+        await handler(ctx)
+        self.assertEqual(["alice"], handled)