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Bug: CORS Support in start-api #4991

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merged 9 commits into from
May 18, 2023
Merged

Bug: CORS Support in start-api #4991

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e02f4f2
handle cors response "Access-Control-Allow-Origin"
sleepwithcoffee Mar 31, 2023
3bb9360
reformat files
sleepwithcoffee Mar 31, 2023
d250973
Merge remote-tracking branch 'upstream/develop' into develop
sleepwithcoffee Apr 8, 2023
2cadadf
Merge branch 'develop' into 4161_cors_origin_headers
sleepwithcoffee Apr 10, 2023
0117c32
Merge remote-tracking branch 'upstream/develop' into develop
sleepwithcoffee Apr 23, 2023
81b5f57
Merge remote-tracking branch 'upstream/develop' into develop
sleepwithcoffee May 6, 2023
af3abe6
Merge branch 'develop' into 4161_cors_origin_headers
sleepwithcoffee May 6, 2023
40674dd
Merge branch 'develop' into 4161_cors_origin_headers
sleepwithcoffee May 6, 2023
912b2bc
minor revert
sleepwithcoffee May 6, 2023
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26 changes: 26 additions & 0 deletions samcli/local/apigw/local_apigw_service.py
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Original file line number Diff line number Diff line change
Expand Up @@ -640,6 +640,7 @@ def _request_handler(self, **kwargs):

route: Route = self._get_current_route(request)
cors_headers = Cors.cors_to_headers(self.api.cors)
cors_headers = self._response_cors_headers(request, cors_headers)
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Thanks for creating this PR! Did we need to restrict this behaviour to only run for HTTP APIs? From the docs and the linked issue, this seems to be something that the Lambda function deals with on for REST, but we would need to manage for HTTP.

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hi @lucashuy

During the implementation, I referred to MDN web docs for reference:

image

I also referred to the implementation of middy cors middleware

below piece of code will basically parse and return a single origin if matched:
image

it is explained if looking deeper into the getOrigin() function:

image

Hope these help explain the reasoning behind my code.

Thanks,

lambda_authorizer = route.authorizer_object

# payloadFormatVersion can only support 2 values: "1.0" and "2.0"
Expand Down Expand Up @@ -800,6 +801,31 @@ def _get_current_route(self, flask_request):

return route

@staticmethod
def _response_cors_headers(flask_request, cors_headers):
if "Access-Control-Allow-Origin" not in cors_headers:
return cors_headers

cors_origins = cors_headers["Access-Control-Allow-Origin"]
# unset this header due to restrictive manner
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Why unset this? It looks like it should be removed in the case that response_allowed_origin is not set. If so, I would move this to be closer to line 437. I think it just make it a little easier to read since the mutation of the cors_headers is all in one spot.

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Hi @jfuss , thank you for taking your time to review this

we unset and set again if a match is found (restrictive manner)

if multiple domains are allowed, we only send back 1 allowed domain in our response header
if all domains are allowed, we also only send back 1 allowed domain in our response header

we do not return this header (implying a deny) if no matches is found

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hi @jfuss please also refer to my below comment:
#4991 (comment)

del cors_headers["Access-Control-Allow-Origin"]

incoming_origin = flask_request.headers.get("Origin")
# Restrictive manner: do not allow any origin by default
response_allowed_origin = None
if incoming_origin:
if cors_origins == "*" and cors_headers.get("Access-Control-Allow-Credentials") is True:
response_allowed_origin = incoming_origin
else:
cors_origins_arr = cors_origins.split(",")
if incoming_origin in cors_origins_arr:
response_allowed_origin = incoming_origin

if response_allowed_origin:
cors_headers["Access-Control-Allow-Origin"] = response_allowed_origin

return cors_headers

@staticmethod
def get_request_methods_endpoints(flask_request):
"""
Expand Down
134 changes: 134 additions & 0 deletions tests/unit/local/apigw/test_local_apigw_service.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1835,6 +1835,140 @@ def test_lambda_output_json_object_no_status_code(self):
self.assertEqual(body, lambda_output)


class TestService_cors_response_headers(TestCase):
def test_response_cors_no_origin(self):
request_mock = Mock()
headers_mock = Mock()
headers_mock.keys.return_value = []
request_mock.headers = headers_mock
request_mock.scheme = "http"

cors = Cors(allow_origin="*", allow_methods="GET,POST,OPTIONS")

response_cors_headers = Cors.cors_to_headers(cors)
response_cors_headers = LocalApigwService._response_cors_headers(request_mock, response_cors_headers)

self.assertTrue("Access-Control-Allow-Origin" not in response_cors_headers)

def test_response_cors_with_origin(self):
incoming_origin = "localhost:3000"

request_mock = Mock()
headers_mock = Mock()
headers_mock.keys.return_value = []
headers_mock.keys.return_value = ["Origin", "Content-Type"]
headers_mock.get.side_effect = [incoming_origin, "application/json"]
headers_mock.getlist.side_effect = [[incoming_origin], ["application/json"]]
request_mock.headers = headers_mock
request_mock.scheme = "http"

cors = Cors(allow_origin="*", allow_methods="GET,POST,OPTIONS", allow_credentials=True)

response_cors_headers = Cors.cors_to_headers(cors)
response_cors_headers = LocalApigwService._response_cors_headers(request_mock, response_cors_headers)

self.assertEqual(incoming_origin, response_cors_headers["Access-Control-Allow-Origin"])

def test_response_cors_with_origin_single_domain(self):
incoming_origin = "localhost:3000"

request_mock = Mock()
headers_mock = Mock()
headers_mock.keys.return_value = []
headers_mock.keys.return_value = ["Origin", "Content-Type"]
headers_mock.get.side_effect = [incoming_origin, "application/json"]
headers_mock.getlist.side_effect = [[incoming_origin], ["application/json"]]
request_mock.headers = headers_mock
request_mock.scheme = "http"

cors = Cors(allow_origin="localhost:3000", allow_methods="GET,POST,OPTIONS", allow_credentials=True)

response_cors_headers = Cors.cors_to_headers(cors)
response_cors_headers = LocalApigwService._response_cors_headers(request_mock, response_cors_headers)

self.assertEqual(incoming_origin, response_cors_headers["Access-Control-Allow-Origin"])

def test_response_cors_with_origin_multi_domains(self):
incoming_origin = "localhost:3000"

request_mock = Mock()
headers_mock = Mock()
headers_mock.keys.return_value = []
headers_mock.keys.return_value = ["Origin", "Content-Type"]
headers_mock.get.side_effect = [incoming_origin, "application/json"]
headers_mock.getlist.side_effect = [[incoming_origin], ["application/json"]]
request_mock.headers = headers_mock
request_mock.scheme = "http"

cors = Cors(
allow_origin="localhost:3000,localhost:6000", allow_methods="GET,POST,OPTIONS", allow_credentials=True
)

response_cors_headers = Cors.cors_to_headers(cors)
response_cors_headers = LocalApigwService._response_cors_headers(request_mock, response_cors_headers)

self.assertEqual(incoming_origin, response_cors_headers["Access-Control-Allow-Origin"])

def test_response_cors_with_origin_multi_domains_not_matching(self):
incoming_origin = "localhost:3000"

request_mock = Mock()
headers_mock = Mock()
headers_mock.keys.return_value = []
headers_mock.keys.return_value = ["Origin", "Content-Type"]
headers_mock.get.side_effect = [incoming_origin, "application/json"]
headers_mock.getlist.side_effect = [[incoming_origin], ["application/json"]]
request_mock.headers = headers_mock
request_mock.scheme = "http"

cors = Cors(
allow_origin="localhost:4000,localhost:6000", allow_methods="GET,POST,OPTIONS", allow_credentials=True
)

response_cors_headers = Cors.cors_to_headers(cors)
response_cors_headers = LocalApigwService._response_cors_headers(request_mock, response_cors_headers)

self.assertTrue("Access-Control-Allow-Origin" not in response_cors_headers)

def test_response_cors_not_allow_credentials(self):
incoming_origin = "localhost:3000"

request_mock = Mock()
headers_mock = Mock()
headers_mock.keys.return_value = []
headers_mock.keys.return_value = ["Origin", "Content-Type"]
headers_mock.get.side_effect = [incoming_origin, "application/json"]
headers_mock.getlist.side_effect = [[incoming_origin], ["application/json"]]
request_mock.headers = headers_mock
request_mock.scheme = "http"

cors = Cors(allow_origin="*", allow_methods="GET,POST,OPTIONS", allow_credentials=False)

response_cors_headers = Cors.cors_to_headers(cors)
response_cors_headers = LocalApigwService._response_cors_headers(request_mock, response_cors_headers)

self.assertTrue("Access-Control-Allow-Origin" not in response_cors_headers)

def test_response_cors_missing_allow_credentials(self):
incoming_origin = "localhost:3000"

request_mock = Mock()
headers_mock = Mock()
headers_mock.keys.return_value = []
headers_mock.keys.return_value = ["Origin", "Content-Type"]
headers_mock.get.side_effect = [incoming_origin, "application/json"]
headers_mock.getlist.side_effect = [[incoming_origin], ["application/json"]]
request_mock.headers = headers_mock
request_mock.scheme = "http"

cors = Cors(allow_origin="*", allow_methods="GET,POST,OPTIONS")

response_cors_headers = Cors.cors_to_headers(cors)
response_cors_headers = LocalApigwService._response_cors_headers(request_mock, response_cors_headers)

self.assertTrue("Access-Control-Allow-Origin" not in response_cors_headers)


class TestServiceCorsToHeaders(TestCase):
def test_basic_conversion(self):
cors = Cors(
Expand Down