log_context.pl

use Mojolicious::Lite -signatures;

sub _generate_id { ... }

{
  package Mojo::Log::WithContext;
  use Mojo::Base 'Mojo::Log', -signatures;
  has context => sub { {} };
  has id      => sub { _generate_id() };
  has format  => sub { sub ($id, $first, @lines) { ("[$id] $first", @lines) } };
  has parent  => sub { Mojo::Log->new };

  sub new {
    my $self = shift->SUPER::new(@_);
    $self->unsubscribe('message');
    $self->on(message => sub ($self, $level, @lines) {
      $self->parent->$level($self->format->($self->id, @lines));
    });
    return $self;
  }
}

# this would be an attribute on the controller really
helper log => sub ($c) {
  $c->stash->{logger} ||= Mojo::Log::WithContext->new(
    id     => $c->req->request_id,
    parent => $c->app->log,
  );
};

get '/' => sub ($c) {
  $c->log->info('Requested /'); # log some message
  $c->render(text => 'done');
};

app->start;