add default CORS middleware (#441)

* add default CORS middleware

* test that default cors middleware is working

stac_fastapi/api/stac_fastapi/api/app.py

@@ -14,7 +14,7 @@
 from starlette.responses import JSONResponse, Response
 
 from stac_fastapi.api.errors import DEFAULT_STATUS_CODES, add_exception_handlers
-from stac_fastapi.api.middleware import ProxyHeaderMiddleware
+from stac_fastapi.api.middleware import CORSMiddleware, ProxyHeaderMiddleware
 from stac_fastapi.api.models import (
     APIRequest,
     CollectionUri,
@@ -93,7 +93,9 @@ class StacApi:
     pagination_extension = attr.ib(default=TokenPaginationExtension)
     response_class: Type[Response] = attr.ib(default=JSONResponse)
     middlewares: List = attr.ib(
-        default=attr.Factory(lambda: [BrotliMiddleware, ProxyHeaderMiddleware])
+        default=attr.Factory(
+            lambda: [BrotliMiddleware, CORSMiddleware, ProxyHeaderMiddleware]
+        )
     )
     route_dependencies: List[Tuple[List[Scope], List[Depends]]] = attr.ib(default=[])
 

stac_fastapi/api/stac_fastapi/api/middleware.py

@@ -1,12 +1,48 @@
 """api middleware."""
-
 import re
+import typing
 from http.client import HTTP_PORT, HTTPS_PORT
 from typing import List, Tuple
 
+from starlette.middleware.cors import CORSMiddleware as _CORSMiddleware
 from starlette.types import ASGIApp, Receive, Scope, Send
 
 
+class CORSMiddleware(_CORSMiddleware):
+    """
+    Subclass of Starlette's standard CORS middleware with default values set to those reccomended by the STAC API spec.
+
+    https://github.com/radiantearth/stac-api-spec/blob/914cf8108302e2ec734340080a45aaae4859bb63/implementation.md#cors
+    """
+
+    def __init__(
+        self,
+        app: ASGIApp,
+        allow_origins: typing.Sequence[str] = ("*",),
+        allow_methods: typing.Sequence[str] = (
+            "OPTIONS",
+            "POST",
+            "GET",
+        ),
+        allow_headers: typing.Sequence[str] = ("Content-Type",),
+        allow_credentials: bool = False,
+        allow_origin_regex: typing.Optional[str] = None,
+        expose_headers: typing.Sequence[str] = (),
+        max_age: int = 600,
+    ) -> None:
+        """Create CORS middleware."""
+        super().__init__(
+            app,
+            allow_origins,
+            allow_methods,
+            allow_headers,
+            allow_credentials,
+            allow_origin_regex,
+            expose_headers,
+            max_age,
+        )
+
+
 class ProxyHeaderMiddleware:
     """
     Account for forwarding headers when deriving base URL.

stac_fastapi/api/tests/test_middleware.py

@@ -1,7 +1,13 @@
+from unittest import mock
+
 import pytest
 from starlette.applications import Starlette
+from starlette.testclient import TestClient
 
+from stac_fastapi.api.app import StacApi
 from stac_fastapi.api.middleware import ProxyHeaderMiddleware
+from stac_fastapi.types.config import ApiSettings
+from stac_fastapi.types.core import BaseCoreClient
 
 
 @pytest.fixture
@@ -10,6 +16,13 @@ def proxy_header_middleware() -> ProxyHeaderMiddleware:
     return ProxyHeaderMiddleware(app)
 
 
+@pytest.fixture
+def test_client() -> TestClient:
+    app = StacApi(settings=ApiSettings(), client=mock.create_autospec(BaseCoreClient))
+    with TestClient(app.app) as client:
+        yield client
+
+
 @pytest.mark.parametrize(
     "headers,key,expected",
     [
@@ -138,3 +151,9 @@ def test_get_forwarded_url_parts(
 ):
     actual = proxy_header_middleware._get_forwarded_url_parts(scope)
     assert actual == expected
+
+
+def test_cors_middleware(test_client):
+    resp = test_client.get("/_mgmt/ping", headers={"Origin": "http://netloc"})
+    assert resp.status_code == 200
+    assert resp.headers["access-control-allow-origin"] == "*"