Fix CORS configuration for frontend access

- Added custom CORS middleware to ensure headers are always present
- Added explicit OPTIONS handler for preflight requests
- Used both custom and standard CORS middleware for maximum compatibility
- This should definitively resolve CORS blocking issues

main.py

@@ -1,7 +1,8 @@
 import logging
 from contextlib import asynccontextmanager
-from fastapi import FastAPI
+from fastapi import FastAPI, Request, Response
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.middleware.base import BaseHTTPMiddleware
 from app.db.session import engine
 from app.db.base import Base
 from app.routers import monitors, checks, scheduler
@@ -15,6 +16,33 @@ logger = logging.getLogger(__name__)
 Base.metadata.create_all(bind=engine)
 
 
+class CORSMiddleware2(BaseHTTPMiddleware):
+    async def dispatch(self, request: Request, call_next):
+        # Handle preflight requests
+        if request.method == "OPTIONS":
+            response = Response()
+            response.headers["Access-Control-Allow-Origin"] = "*"
+            response.headers["Access-Control-Allow-Methods"] = (
+                "GET, POST, PUT, DELETE, OPTIONS"
+            )
+            response.headers["Access-Control-Allow-Headers"] = "*"
+            response.headers["Access-Control-Max-Age"] = "3600"
+            return response
+
+        # Process the request
+        response = await call_next(request)
+
+        # Add CORS headers to the response
+        response.headers["Access-Control-Allow-Origin"] = "*"
+        response.headers["Access-Control-Allow-Methods"] = (
+            "GET, POST, PUT, DELETE, OPTIONS"
+        )
+        response.headers["Access-Control-Allow-Headers"] = "*"
+        response.headers["Access-Control-Expose-Headers"] = "*"
+
+        return response
+
+
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     # Startup
@@ -34,6 +62,10 @@ app = FastAPI(
     lifespan=lifespan,
 )
 
+# Add custom CORS middleware
+app.add_middleware(CORSMiddleware2)
+
+# Also add the standard CORS middleware as backup
 app.add_middleware(
     CORSMiddleware,
     allow_origins=["*"],
@@ -63,10 +95,17 @@ async def health_check():
     return {"status": "healthy", "service": "uptime-monitoring-api"}
 
 
-@app.options("/{path:path}")
+@app.options("/{full_path:path}")
-async def options_handler():
+async def options_handler(full_path: str):
     """Handle preflight OPTIONS requests"""
-    return {"message": "OK"}
+    from fastapi import Response
+
+    response = Response()
+    response.headers["Access-Control-Allow-Origin"] = "*"
+    response.headers["Access-Control-Allow-Methods"] = "GET, POST, PUT, DELETE, OPTIONS"
+    response.headers["Access-Control-Allow-Headers"] = "*"
+    response.headers["Access-Control-Max-Age"] = "3600"
+    return response
 
 
 if __name__ == "__main__":