Fix issue where CORS headers were not being returned properly

Author: suecharo

sapporo/app.py

@@ -8,7 +8,10 @@
 from fastapi.exceptions import RequestValidationError
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse
+from starlette.datastructures import Headers, MutableHeaders
 from starlette.exceptions import HTTPException as StarletteHTTPException
+from starlette.responses import PlainTextResponse, Response
+from starlette.types import ASGIApp, Message, Receive, Scope, Send
 
 from sapporo.auth import get_auth_config
 from sapporo.config import (LOGGER, PKG_DIR, add_openapi_info, get_config,
@@ -59,6 +62,52 @@ async def generic_exception_handler(_request: Request, _exc: Exception) -> JSONR
         )
 
 
+class CustomCORSMiddleware(CORSMiddleware):
+    """\
+    CORSMiddleware that returns CORS headers even if the Origin header is not present
+    """
+
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        if scope["type"] != "http":
+            await self.app(scope, receive, send)
+            return
+
+        method = scope["method"]
+        headers = Headers(scope=scope)
+
+        if method == "OPTIONS" and "access-control-request-method" in headers:
+            response = self.preflight_response(request_headers=headers)
+            await response(scope, receive, send)
+            return
+
+        await self.simple_response(scope, receive, send, request_headers=headers)
+
+    async def send(
+        self, message: Message, send: Send, request_headers: Headers
+    ) -> None:
+        if message["type"] != "http.response.start":
+            await send(message)
+            return
+
+        message.setdefault("headers", [])
+        headers = MutableHeaders(scope=message)
+        headers.update(self.simple_headers)
+        origin = request_headers.get("Origin", "*")
+        has_cookie = "cookie" in request_headers
+
+        # If request includes any cookie headers, then we must respond
+        # with the specific origin instead of '*'.
+        if self.allow_all_origins and has_cookie:
+            self.allow_explicit_origin(headers, origin)
+
+        # If we only allow specific origins, then we have to mirror back
+        # the Origin header in the response.
+        elif not self.allow_all_origins and self.is_allowed_origin(origin=origin):
+            self.allow_explicit_origin(headers, origin)
+
+        await send(message)
+
+
 def init_app_state() -> None:
     """
     Perform validation, initialize the cache, and log the configuration contents.
@@ -146,9 +195,8 @@ def create_app() -> FastAPI:
     )
 
     app.add_middleware(
-        CORSMiddleware,
+        CustomCORSMiddleware,
         allow_origins=[app_config.allow_origin],
-        allow_credentials=True,
         allow_methods=["*"],
         allow_headers=["*"],
     )