Package User

sub new {
  my ($class, $username) = @_;
  my $self->{username} = $username;
  # connect to server and store connection details in $self->{server}
  bless $self, $class;
}

sub get {
  my $self = shift;
  # call server using $self->{server} adding session_id if we have one
}
  
sub login {
  my $self = shift;
  $self->get('login'); # will store session_id in User object
}

sub get_accounts {
  my $self = shift;
  return $self->get('accounts');
}

sub open_account {
  my ($self, $account_id) = @_;
  my $self->{account} = User::Account->new(account_id);
  return $self->{account};
}

Package Account

our @ISA = qw(User);

sub balance {
  # needs to call User::get but does not have session id or server info
}