c2-core: add CORS middleware so the browser can call the REST API (#110)

The Archive page's GET /calls/search failed its CORS preflight (OPTIONS -> 405, no Access-Control-* headers). Allow the app origin(s) explicitly for the standard methods and the authorization/content-type headers.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Claude-Session: https://claude.ai/code/session_01Tbknwttzou4s46PAykmtix

drb-c2-core/.env.example

@@ -33,6 +33,13 @@ SUMMARY_INTERVAL_MINUTES=15
 CORRELATION_WINDOW_HOURS=4
 EMBEDDING_SIMILARITY_THRESHOLD=0.82
 
+# Browser origins allowed to call this API cross-origin (JSON list). The only
+# browser caller is the frontend's Archive page (GET /calls/search). Set this
+# to the exact origin the frontend is served from — scheme + host, no path.
+# Defaults to https://drb.cusano.net. A "*" entry works for local dev but is
+# logged as a probable misconfiguration and never gets a credentialed response.
+CORS_ORIGINS=["https://drb.cusano.net"]
+
 # Fleet-wide token edge nodes present as X-Enrollment-Token on first boot
 # (POST /nodes/enroll). Shared across every node — NOT a per-node secret.
 # Generate with: openssl rand -hex 32

drb-c2-core/app/config.py

@@ -180,16 +180,18 @@ class Settings(BaseSettings):
     # between genuinely separate transmissions on a busy dispatch channel.
     duplicate_window_seconds: int = 10
 
-    # CORS — set to your frontend origin(s) in production, e.g. ["https://app.example.com"]
-    # Defaults to "*" for local development only.
+    # Browser origins allowed to call this API cross-origin. The only browser
+    # caller is the frontend's Archive page (GET /calls/search) — every other
+    # page reads Firestore directly. The frontend is served on the BARE domain
+    # (see infra Caddyfile.j2 — only drb. and api. have DNS records), so the
+    # default is that origin, not app.<domain>. Override via CORS_ORIGINS (JSON
+    # list) if the frontend ever moves; keep infra/.../c2-core.env.j2 in sync.
     #
-    # Leaving this as "*" is not merely permissive: main.py turns OFF
-    # allow_credentials when it sees a wildcard, because Starlette would
-    # otherwise reflect each caller's origin back WITH
-    # Access-Control-Allow-Credentials. So a production deployment that
-    # forgets to set this gets a loud ERROR at startup and loses credentialed
-    # cross-origin requests, rather than silently accepting every origin.
-    cors_origins: list[str] = ["*"]
+    # A "*" entry here still works for local dev but is refused a credentialed
+    # response: main.py never enables allow_credentials (auth is a Bearer
+    # header, not a cookie), and it logs a loud ERROR when it sees a wildcard
+    # in a deployment so a forgotten override is visible.
+    cors_origins: list[str] = ["https://drb.cusano.net"]
 
     # Discord webhook URL that app/internal/ai_health.py posts to when an AI
     # tier (transcription/correlation) transitions into or out of degraded

drb-c2-core/app/main.py

@@ -78,33 +78,40 @@ async def lifespan(app: FastAPI):
 
 app = FastAPI(title="DRB C2 Core", lifespan=lifespan)
 
-# "*" plus allow_credentials=True is not the permissive-but-harmless setting it
-# looks like. Starlette does not refuse the combination -- it reflects the
-# caller's Origin back and still sends Access-Control-Allow-Credentials: true,
-# so the effective policy becomes "any origin, with credentials", the opposite
-# of what a wildcard normally means. Rather than trust every deployment to
-# remember to override CORS_ORIGINS, make the dangerous pair unrepresentable.
+# The browser needs CORS to reach this API at all: the frontend's Archive page
+# calls GET /calls/search with Authorization + Content-Type headers, which
+# forces a preflight. Without this middleware the OPTIONS gets a bare 405 and
+# the fetch fails (#110). allow_origins is an explicit list -- never "*" in a
+# deployment -- so name every host the frontend is served from in CORS_ORIGINS.
+#
+# allow_credentials stays False on purpose: auth here is a Bearer header, not a
+# cookie, so credentialed CORS is never needed, and keeping it False is what
+# lets an explicit-origin allowlist work without Starlette's "*"-only
+# restriction. "*" + credentials is the dangerous pair (Starlette reflects the
+# caller's Origin back WITH Access-Control-Allow-Credentials: true); this code
+# cannot produce it because credentials are hard-off.
 def cors_allows_credentials(origins: list[str]) -> bool:
-    """False when any entry is a wildcard. Extracted so it can be tested
-    without re-importing this module, which drags in every router."""
-    return "*" not in origins
+    """Always False -- credentialed CORS is never enabled here (Bearer auth,
+    not cookies). Kept as a named predicate so a future edit that wants to
+    turn credentials on has to go through here and confront the "*" case.
+    A wildcard entry would additionally be refused a credentialed response."""
+    return False
 
 
-_cors_is_wildcard = not cors_allows_credentials(settings.cors_origins)
+_cors_is_wildcard = "*" in settings.cors_origins
 if _cors_is_wildcard:
     logger.error(
-        "CORS_ORIGINS is '*', so credentialed cross-origin requests are being "
-        "DISABLED to avoid reflecting every caller's origin back with "
-        "Access-Control-Allow-Credentials. Set CORS_ORIGINS to your frontend "
-        "origin(s) in production, e.g. [\"https://app.example.com\"]."
+        "CORS_ORIGINS contains '*'. That is fine for local dev but is almost "
+        "certainly a misconfigured deployment -- set CORS_ORIGINS to your "
+        "frontend origin(s), e.g. [\"https://drb.cusano.net\"]."
     )
 
 app.add_middleware(
     CORSMiddleware,
     allow_origins=settings.cors_origins,
-    allow_methods=["*"],
-    allow_headers=["*"],
-    allow_credentials=not _cors_is_wildcard,
+    allow_methods=["GET", "POST", "PUT", "PATCH", "DELETE", "OPTIONS"],
+    allow_headers=["authorization", "content-type"],
+    allow_credentials=False,
 )
 
 app.include_router(nodes.router,     dependencies=[Depends(require_service_or_firebase_token)])

drb-c2-core/tests/test_cors.py

@@ -0,0 +1,66 @@
+"""
+End-to-end CORS wiring for the one browser-facing REST surface.
+
+The frontend's Archive page calls GET /calls/search with Authorization +
+Content-Type headers, which forces the browser to send a CORS preflight
+first. Before #110 that OPTIONS got a bare 405 with no Access-Control-*
+headers and the fetch failed with "TypeError: Failed to fetch". These
+tests drive the real app through TestClient so a regression in the
+middleware wiring (not just the helper) is caught.
+
+TestClient is NOT used as a context manager on purpose: that would run the
+lifespan (mqtt_handler.connect(), the sweeper loops, dynsec bootstrap),
+none of which is needed here -- CORSMiddleware answers a preflight before
+routing or dependencies run.
+"""
+from fastapi.testclient import TestClient
+
+from app.config import settings
+from app.main import app
+
+client = TestClient(app)
+
+ALLOWED_ORIGIN = "https://drb.cusano.net"
+DISALLOWED_ORIGIN = "https://evil.example.com"
+
+
+def test_default_allowed_origin_matches_the_deployed_frontend():
+    # The frontend is served on the bare domain (infra Caddyfile.j2), so the
+    # default must allow exactly that origin without any env override.
+    assert ALLOWED_ORIGIN in settings.cors_origins
+
+
+def test_preflight_for_calls_search_is_allowed():
+    resp = client.options(
+        "/calls/search",
+        headers={
+            "Origin": ALLOWED_ORIGIN,
+            "Access-Control-Request-Method": "GET",
+            "Access-Control-Request-Headers": "authorization,content-type",
+        },
+    )
+    assert resp.status_code == 200
+    assert resp.headers.get("access-control-allow-origin") == ALLOWED_ORIGIN
+    allow_methods = resp.headers.get("access-control-allow-methods", "").upper()
+    assert "GET" in allow_methods
+    # Bearer auth, not cookies -- credentials must never be advertised.
+    assert "access-control-allow-credentials" not in resp.headers
+
+
+def test_preflight_from_disallowed_origin_gets_no_allow_origin():
+    resp = client.options(
+        "/calls/search",
+        headers={
+            "Origin": DISALLOWED_ORIGIN,
+            "Access-Control-Request-Method": "GET",
+        },
+    )
+    assert resp.headers.get("access-control-allow-origin") is None
+
+
+def test_simple_get_from_allowed_origin_is_annotated():
+    # Even a non-preflight GET must carry Access-Control-Allow-Origin or the
+    # browser hides the response body from the page.
+    resp = client.get("/health", headers={"Origin": ALLOWED_ORIGIN})
+    assert resp.status_code == 200
+    assert resp.headers.get("access-control-allow-origin") == ALLOWED_ORIGIN

drb-c2-core/tests/test_cors_policy.py

@@ -5,8 +5,9 @@ Starlette does not reject `allow_origins=["*"]` combined with
 `allow_credentials=True`. It reflects the caller's Origin back in
 Access-Control-Allow-Origin and still sends
 Access-Control-Allow-Credentials: true, so the effective policy is the
-opposite of what a wildcard usually means. main.py defuses that by turning
-credentials off whenever it sees a wildcard; these tests hold it to that.
+opposite of what a wildcard usually means. main.py never enables
+credentials at all (auth is a Bearer header, not a cookie), which makes
+that pair unrepresentable; these tests hold it to that.
 
 The policy lives in a pure function so it can be exercised directly --
 reloading app.main to vary settings drags every router back through import
@@ -28,11 +29,11 @@ def test_wildcard_among_real_origins_still_disables_credentials():
     assert cors_allows_credentials(["https://app.example.com", "*"]) is False
 
 
-def test_named_origins_keep_credentials():
-    # Naming your origins is how you ask for credentialed requests, so a
-    # correctly configured deployment must not be penalised.
-    assert cors_allows_credentials(["https://app.example.com"]) is True
-    assert cors_allows_credentials([]) is True
+def test_credentials_never_enabled_even_for_named_origins():
+    # Auth here is a Bearer header, not a cookie, so credentialed CORS is
+    # never needed. The predicate is hard-off regardless of the origin list.
+    assert cors_allows_credentials(["https://app.example.com"]) is False
+    assert cors_allows_credentials([]) is False
 
 
 def test_the_app_actually_mounted_that_policy():
@@ -42,6 +43,7 @@ def test_the_app_actually_mounted_that_policy():
         (mw.kwargs for mw in app.user_middleware if mw.cls is CORSMiddleware), None
     )
     assert opts is not None, "CORSMiddleware is not mounted at all"
+    assert opts["allow_credentials"] is False
     assert opts["allow_credentials"] is cors_allows_credentials(settings.cors_origins)