A word of warning: Your Foursquare API client ID and Secret are completely visible to anyone and can easily be abused. [1]
Also, currently the client ID is exceeding its rate limit, so I cannot add my own locations.
[1] You are making these kinds of requests: https://api.foursquare.com/v2/venues/suggestCompletion?query...
Maybe proxy your Foursquare API requests via https://www.eliotand.me/airbnb-poster/search or a similar API endpoint you'd create. Disallow CORS on that new API endpoint. You can keep the API call signature but remove the client ID and secret.
On your backend you can then make those Foursquare API requests and add the client ID and secret to the request.
You could also do this simply by running on Azure Functions (free consumption plan). All you need to deploy is a simple proxies.json, see [1].
On the AWS side it appears you can entirely use API Gateway. Here [2] is a Swagger 2.0 definition file I just wrote which upon import creates an API endpoint that should proxy requests to an external API while adding your secret credentials.
[1]: https://aka.ms/apiproxy [2]: https://gist.github.com/berndverst/b59fa0b38544f13c05ae0b77f...
https://gist.github.com/berndverst/37d87570418bbee77641777e1...