using RestSharp;
using System;
using System.Text;

var credentials = Convert.ToBase64String(Encoding.UTF8.GetBytes("{EMAIL}:{PASSWORD}"));

var client = new RestClient("https://api.keygen.sh/v1/accounts/{ACCOUNT}");
var request = new RestRequest("tokens", Method.POST);

request.AddHeader("Accept", "application/vnd.api+json");
request.AddHeader("Authorization", $"Basic {credentials}");

var response = client.Execute(request);