If I add a validation attribute:

public class ProductDownloadListModel
{        
    //xxxxx-xxxxx-xxxxx
    [Required]
    [StringLength(17)]
    public string PSN { get; set; }
    public DateTime PsnExpirationDate { get; set; } 
    public DataTable Downloads { get; set; } 

}

and the user enters a 17-character string but includes white space on the end, I get a validation error because the string is greater than that specified by the [StringLength(17)] attribute. How can I prevent this? I'd prefer not to have to have javaScript trim the string before submits.