Route requests through local proxy with CORS

[u8sand]

Because VSCode has no intention of changing their stance on required CORS headers to work in webviews microsoft/vscode#72900 -- the only workaround I see is using a proxy service like http://www.whateverorigin.org/ which just proxies requests and adds CORS headers.

Fortunately this app is in a unique place in that it's already running a webserver. So we can use that same server to proxy requests and add CORS. This is pretty easy with SwaggerUIBundle's requestInterceptor config argument which takes a function for altering requests.

Thus this PR does two things:

• add a /proxy endpoint to the server which takes a query param url with the actual URL. use request library to forward the entire request object to that url. Add CORS to the response and return it.
• add requestInterceptor argument to SwaggerUIBundle to change the url to use the backend's /proxy?url=...

The result -- no need to worry about CORS, the UI works the same.

Fixes #30
Fixes #23

Edit: Since this has been here for a while; if anyone is interested in using this now it can be done with the release on my fork where I have included the compiled vsix file: https://github.com/MaayanLab/vs-swagger-viewer/releases if you do use it, let me know if you find any issues.

Edit: Updated a bit to fix an issue with POST requests

• eliminate request as a dependency, using instead http and https
• Instead of the query parameter url which may also cause conflicts, we always POST to /proxy serializing the url, method, headers, and body with json

Edit: A bug in the last fix broke querystrings 🤦 this was fixed.

• pass url directly to request instead of trying to rebuild it in the options

[kitarikes]

Thanks to you, I was able to resolve the error！

[kitarikes]

I did notice one problem.

In the swagger preview, the request is made as a POST, but when I checked the API server log, I noticed that the request was rewritten as a GET (probably by a script that avoids cors).

So anything other than GET requests won't work properly.

[u8sand]

This should be an easy fix, i can do it later today. Thanks for reporting.

Edit: I've updated it, the PR comment, merged with upstream and re-released.