public IObservable <Result <SessionEntity> > CreateSession(ValidateTokenPostCommand command) =>
 _sessionRemoteDataSource.CreateRequestToken()
 .ExtractResult()
 .Select(token =>
         new ValidateTokenPostCommand(
             command.Username, command.Password, token.RequestToken.Value))
 .SelectMany(validateCommand =>
             _sessionRemoteDataSource.ValidateRequestToken(validateCommand))
 .ExtractResult()
 .Select(validation =>
 public IObservable <Result <TokenValidationDto> > ValidateRequestToken(ValidateTokenPostCommand command) =>
 Api.ValidateRequestToken(command).ToResult();