public virtual IssuedToken IssueToken(string consumerKey)
        {
            string token = Guid.NewGuid().ToString();

            var tokenData = new IssuedToken
                                {
                                    Token = token,
                                    TokenSecret = Guid.NewGuid().ToString(),
                                    ConsumerKey = consumerKey
                                };

            _tokens[token] = tokenData;

            return tokenData;
        }
 public virtual bool IsUsable(IssuedToken token)
 {
     return (!token.Expires.HasValue || (token.Expires.Value >= DateTime.Now))
            && (token.AllowableUses != AllowableTokenUses.None);
 }