Explicitly set CORS headers

By default FastAPI only replies with CORS headers when an origin is
sent. This means that the response should be sent with Vary: Origin,
but it isn't. If this header were added it would reduce cachability.

When we always send the headers this means that the response can be
cached regardless of origin, and CORS are always present.

tilekiln/server/__init__.py

@@ -4,7 +4,6 @@
 import psycopg
 import psycopg_pool
 from fastapi import FastAPI, Response, HTTPException
-from fastapi.middleware.cors import CORSMiddleware
 
 import tilekiln
 from tilekiln.config import Config
@@ -22,25 +21,17 @@
 TILEKILN_URL = "TILEKILN_URL"
 TILEKILN_THREADS = "TILEKILN_THREADS"
 
-STANDARD_HEADERS: dict[str, str] = {}
+STANDARD_HEADERS: dict[str, str] = {"Access-Control-Allow-Origin": "*",
+                                    "Access-Control-Allow-Methods": "GET, HEAD"}
 
 kiln: Kiln
 config: Config
 storage: Storage
 tilesets: dict[str, Tileset] = {}
 
 # Two types of server are defined - one for static tiles, the other for live generated tiles.
-
 server = FastAPI()
-server.add_middleware(CORSMiddleware,
-                      allow_origins=["*"],
-                      allow_methods=["*"],
-                      allow_headers=["*"])
 live = FastAPI()
-live.add_middleware(CORSMiddleware,
-                    allow_origins=["*"],
-                    allow_methods=["*"],
-                    allow_headers=["*"])
 
 
 # TODO: Move elsewhere