Got it to work with this code:
var domain = new Uri("[MY DOMAIN]");
var client = new RestClient(domain);
var request = new RestRequest("oauth/token", DataFormat.None);
request.Method = Method.POST;
request.AddParameter("grant_type", "password");
request.AddParameter("client_id", "[MY CLIENT ID]");
request.AddParameter("client_secret","[MYCLIENT SECRET]");
request.AddParameter("scope", "openid");
request.AddParameter("username", Email);
request.AddParameter("password", Password);
var result = await client.ExecuteAsync(request);
And key was to also do this:
https://www.youtube.com/watch?v=Qc2QAoVfjn0