Unity function to parse GET query parameters from a URL, in lieu of System.Net.Http.HttpClient.ParseQueryString.

ParseUrlQuery.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using UnityEngine.Networking;

...

static Dictionary<string, string> ParseUrlQuery(string url)
{
    var regex = new Regex("[?&]([^=]+)=([^&]*)");
    var query = new Uri(url).Query;

    return regex.Matches(query).ToDictionary(
        static match => match.Groups[1].Value,
        static match => UnityWebRequest.UnEscapeURL(match.Groups[2].Value)
    );
}