Fix authentication with remote kernels

[aminya]

Fixes #2109

[todo]

use @aminya/xmlhttprequest

hydrogen/lib/ws-kernel-picker.ts

Lines 7 to 10 in decb6ad

	import { XMLHttpRequest as NodeXMLHttpRequest } from "xmlhttprequest"; // TODO use @aminya/xmlhttprequest
	import { URL } from "url";
	import { Kernel, Session, ServerConnection } from "@jupyterlab/services";
	import Config from "./config";

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This comment was generated by todo based on a TODO comment in decb6ad in #2110. cc @nteract.