express-http-proxy still gets blocked by CORS policy

I have an express server statically serving my Polymer project. I have a REST API query that I need to make, but if I make it from the client it will be blocked by CORS. So I used express-http-proxy to try to get around that; I send my request to it, and it redirects to the server that has the REST API endpoint on it. This is the entirety of my server code that's running with node server.js:

var express = require('express');
var proxy = require('express-http-proxy');

var server = express();
server.use('/', express.static(__dirname + '/'));
server.listen(8080);
server.use('/rest/api/2/search', proxy('restserver:8877'));
console.log("Server listening on localhost:8080");

When I access restserver:8877/rest/api/2/search in a browser it returns a bunch of json as a 'default' search.

On the client side, I have iron-ajax making this request:

<iron-ajax
            id="getBugs"
            url="/rest/api/2/search"
            params=''
            on-response="handleResponse"
            debounce-duration="300">
        </iron-ajax>

And in the script section, I'm using this.$.getBugs.generateRequest() in the ready function to send the request. So I load this up, expecting the request to not be blocked by CORS, since... it's being proxied by the server. Instead, Chrome devtools gives me this:

XMLHttpRequest cannot load http://restserver:8877/secure/MyJiraHome.jspa. Redirect from 'http://restserver:8877/secure/MyJiraHome.jspa' to 'http://restserver:8877/secure/Dashboard.jspa' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access.

I don't understand why it's giving me those URLs, since I never reference them, and why it's blocking due to CORS, since it's going from the server, not the client, that being the whole point of the proxy.

from express-http-proxy still gets blocked by CORS policy