Conversão de exemplo de autenticação de C# para VB.Net

using System;
using System.Security.Cryptography.X509Certificates;
using System.Collections.Generic;
using RestSharp;

namespace PixGerencianet
{
class Authorize
{
public static string Base64Encode(string plainText)
{
var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
return System.Convert.ToBase64String(plainTextBytes);
}

static void Main(string[] args)
{

var credencials = new Dictionary{
{"client_id", "YOUR-CLIENT-ID"},
{"client_secret", "YOUR-CLIENT-SECRET"}
};
var authorization = Base64Encode(credencials["client_id"] + ":" + credencials["client_secret"]);
var client = new RestSharp.RestClient("https://api-pix-h.gerencianet.com.br/oauth/token");
var request = new RestRequest(Method.POST);

X509Certificate2 uidCert = new X509Certificate2("./certificado.p12", "");
client.ClientCertificates = new X509CertificateCollection() { uidCert };

request.AddHeader("Authorization", "Basic " + authorization);
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\r\n \"grant_type\": \"client_credentials\"\r\n}", ParameterType.RequestBody);

IRestResponse restResponse = client.Execute(request);
string response = restResponse.Content;

Console.WriteLine(response);
}
}
}