test.cs

 public sealed class BearerToken
 {
     [JsonProperty(PropertyName = "access_token")]
     public string AccessToken { get; set; }

     [JsonProperty(PropertyName = "token_type")]
     public string TokenType { get; set; }

     [JsonProperty(PropertyName = "expires_in")]
     public int ExpiresInMilliseconds { get; set; }
 }