private void CheckUsername(string username)
{
if (Identities.Any(x => String.Equals(x.Username, username, StringComparison.InvariantCultureIgnoreCase)))
{
throw new DuplicateUsernameException("The username '" + username + "' is already in use.");
}
}
/// <summary>
/// Returns true if an Identity exists with the username.
/// </summary>
public bool UsernameIsTaken(string username)
{
var value = username.ToUpperInvariant();
return(Identities.Any(x => x.Username == value));
}