feat: RFCP MVP deployed on VPS

Iteration 1:
- Dark theme with 3-way toggle
- Dynamic heatmap gradient (blue→red)
- Radius up to 100km
- Save & Calculate workflow

Iteration 2:
- Terrain overlay toggle
- Batch height operations
- Zoom-dependent heatmap rendering

Infrastructure:
- Backend FastAPI on 8888
- Frontend static build via Caddy
- Systemd services
- Caddy reverse proxy integration

backend/venv/lib/python3.12/site-packages/starlette/middleware/sessions.py

@@ -0,0 +1,85 @@
+from __future__ import annotations
+
+import json
+from base64 import b64decode, b64encode
+from typing import Literal
+
+import itsdangerous
+from itsdangerous.exc import BadSignature
+
+from starlette.datastructures import MutableHeaders, Secret
+from starlette.requests import HTTPConnection
+from starlette.types import ASGIApp, Message, Receive, Scope, Send
+
+
+class SessionMiddleware:
+    def __init__(
+        self,
+        app: ASGIApp,
+        secret_key: str | Secret,
+        session_cookie: str = "session",
+        max_age: int | None = 14 * 24 * 60 * 60,  # 14 days, in seconds
+        path: str = "/",
+        same_site: Literal["lax", "strict", "none"] = "lax",
+        https_only: bool = False,
+        domain: str | None = None,
+    ) -> None:
+        self.app = app
+        self.signer = itsdangerous.TimestampSigner(str(secret_key))
+        self.session_cookie = session_cookie
+        self.max_age = max_age
+        self.path = path
+        self.security_flags = "httponly; samesite=" + same_site
+        if https_only:  # Secure flag can be used with HTTPS only
+            self.security_flags += "; secure"
+        if domain is not None:
+            self.security_flags += f"; domain={domain}"
+
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        if scope["type"] not in ("http", "websocket"):  # pragma: no cover
+            await self.app(scope, receive, send)
+            return
+
+        connection = HTTPConnection(scope)
+        initial_session_was_empty = True
+
+        if self.session_cookie in connection.cookies:
+            data = connection.cookies[self.session_cookie].encode("utf-8")
+            try:
+                data = self.signer.unsign(data, max_age=self.max_age)
+                scope["session"] = json.loads(b64decode(data))
+                initial_session_was_empty = False
+            except BadSignature:
+                scope["session"] = {}
+        else:
+            scope["session"] = {}
+
+        async def send_wrapper(message: Message) -> None:
+            if message["type"] == "http.response.start":
+                if scope["session"]:
+                    # We have session data to persist.
+                    data = b64encode(json.dumps(scope["session"]).encode("utf-8"))
+                    data = self.signer.sign(data)
+                    headers = MutableHeaders(scope=message)
+                    header_value = "{session_cookie}={data}; path={path}; {max_age}{security_flags}".format(
+                        session_cookie=self.session_cookie,
+                        data=data.decode("utf-8"),
+                        path=self.path,
+                        max_age=f"Max-Age={self.max_age}; " if self.max_age else "",
+                        security_flags=self.security_flags,
+                    )
+                    headers.append("Set-Cookie", header_value)
+                elif not initial_session_was_empty:
+                    # The session has been cleared.
+                    headers = MutableHeaders(scope=message)
+                    header_value = "{session_cookie}={data}; path={path}; {expires}{security_flags}".format(
+                        session_cookie=self.session_cookie,
+                        data="null",
+                        path=self.path,
+                        expires="expires=Thu, 01 Jan 1970 00:00:00 GMT; ",
+                        security_flags=self.security_flags,
+                    )
+                    headers.append("Set-Cookie", header_value)
+            await send(message)
+
+        await self.app(scope, receive, send_wrapper)