A generic class that can call REST services and parse their JSON output, or process the deserialized version of the JSON output.

GenericJsonApiClient.cs

namespace GenericRestTools
{
    using Newtonsoft.Json;
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Net.Http;
    using System.Text;
    using System.Threading.Tasks;

    public class GenericJsonApiClient
    {
        public async Task<TExpected> Get<TRequest, TExpected>(TRequest request,
            Func<TRequest, Uri> uriBuilder)
        {
            var uri = uriBuilder(request);

            var client = new HttpClient();
            var msg = new HttpRequestMessage(HttpMethod.Get, uri);
            var response = await client.SendAsync(msg);
            var content = await response.Content.ReadAsStringAsync();

            return JsonConvert.DeserializeObject<TExpected>(content);
        }

        public async Task<GenericJsonApiClient> Get<TRequest, TExpected>(TRequest request,
            Func<TRequest, Uri> uriBuilder,
            Action<TExpected> processor = null)
        {
            var result = await Get<TRequest, TExpected>(request, uriBuilder);

            if (processor != null)
                processor(result);

            return this;
        }
    }
}

SampleCall.cs

var request = new CustomerRequest
{
    Id = 42
};

await new GenericJsonApiClient().Get<CustomerRequest, List<CustomerResponse>>(request, 
    (query) =>
        {
            return new Uri(string.Format("http://mysite.com/api/customer/{0}",
                query.Id)
                );
        }, 
    (customers) =>
        {
            customers.ForEach(r =>
                {
                    Console.WriteLine("{0} {1}, {2}",
                        r.FirstName,
                        r.LastName);
                });
        });