Are multiple HTTP headers with the same name supported? - node.js

Question

I'm experimenting with migrating an ASP.net REST backend to Azure Functions. My possibly naive approach to this was creating a catch-all function that proxies HTTP requests via Node's http module, then slowly replacing endpoints with native Azure Functions with more specific routes. I'm using the CLI, and created a Node function like so:
var http = require("http")
module.exports = function (context, req) {
var body = new Buffer([])
var headers = req.headers
headers["host"] = "my.proxy.target"
var proxy = http.request({
hostname: "my.proxy.target",
port: 80,
method: req.method,
path: req.originalUrl,
headers: headers
}, function(outboundRes) {
console.log("Got response")
context.res.status(outboundRes.statusCode)
for(header in outboundRes.headers) {
console.log("Header", header)
if(header != "set-cookie")
context.res.setHeader(header, outboundRes.headers[header])
else
console.log(outboundRes.headers[header])
}
outboundRes.addListener("data", function(chunk) {
body = Buffer.concat([body, chunk])
})
outboundRes.addListener("end", function() {
console.log("End", context.res)
context.res.raw(body)
})
})
proxy.end(req.body)
}
This almost seems to work, but my backend sets several cookies using several Set-Cookie headers. Node hands these back as an array of cookie values, but it seems like Azure Functions doesn't accept arrays as values, or doesn't permit setting multiple headers with the same name, as seems to be allowed for Set-Cookie.
Is this supported? I've googled and have checked out the TypeScript source for Response, but it doesn't appear to be.
If this isn't supported, what Azure platform services should I use to fail over 404s from one app to another, so I can slowly replace the monolith with Functions? Function proxies would work if I could use them as fallbacks, but that doesn't appear possible.
Thanks!