I use lambda as backend for AWS API Gateway with lambda proxy integration and want to add CORS into response header.
According to documentation:
http://docs.aws.amazon.com/apigateway/latest/developerguide/how-to-cors.html
However, you must rely on the back end to return the Access-Control-Allow-Origin headers because the integration response is disabled for the proxy integration.
How can I program it in my lambda function with Python.
To create OPTIONS method you can enable it from the Gateway
It will create a method OPTIONS on the resource(endpoint)
for GET/POST other HTTP Verbs you will need to manage it from your code, in case of python
return {
'statusCode': "200",
'body': json.dumps({"test" : "123"}),
'headers': {
"Content-Type" : "application/json",
"Access-Control-Allow-Origin" : "*",
"Allow" : "GET, OPTIONS, POST",
"Access-Control-Allow-Methods" : "GET, OPTIONS, POST",
"Access-Control-Allow-Headers" : "*"
}
}
for other unhandled cases like IntegrationTimeout (504) or Error in your code (502), you can configure default response headers at API Gateway Level. refer Default Response Headers: AWS API Gateway w/ Proxy Integration
you need to add a method "options" to your api gateway and using a proxy lambda... return
result.headers = { "Access-Control-Allow-Origin": "domain.com" }
so when the browser will first call options to your server it will return the CORS headers.
the thing is that, by default your lambda method will be called for "any" method, so you need to change the default one to get,post or whatever you need
note: you could also use the same method, like any or options,get,post and if it is a options call, only return status 200 and the cors header. it depends if you are using or not an auth method for get,post,etc
there is an option in Lambda console "Enable CORS" if you are just using lambda with nothing strange
If you use Mangum and FastAPI you can override the headers of the response by defining a custom class:
from fastapi import FastAPI
class AWSMangum(Mangum):
"""
It overwrites the __call__ method of the Mangum class to add CORS headers to the response.
"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def __call__(self, *args, **kwargs):
response = super().__call__(*args, **kwargs)
logger.info(response)
response["headers"]["Access-Control-Allow-Origin"] = "*"
return response
app = FastAPI(...)
handler = AWSMangum(app)
