The SortDirection enum (https://github.com/octokit/octokit.net/blob/master/Octokit/Models/Request/IssueRequest.cs#L91) values has a Parameter(Value="") attribute applied to it so we could create an Enum extensions class and implement this:

    public static string ToParameter(this Enum prop)
    {
        if (prop == null) return null;

        var member = prop.GetType().GetMember(prop.ToString()).FirstOrDefault();
        if (member == null) return null;

        var attribute = member.GetCustomAttributes(typeof(ParameterAttribute), false)
            .Cast<ParameterAttribute>()
            .FirstOrDefault();

        return attribute != null ? attribute.Value : null;
    }

Then we can just do `Order.ToParameter` and that will convert it to the correct query parameter value.