I am considering installing TwigBridge into October so i can access Laravel features such as Form, Auth ect. but i am not sure if it is "bad practice" accessing, classes such as Auth from the Twig template? is it better to keep the templates sterile and do everything in the controller?

Any views on this?

I think you'll find most of them are already included, otherwise you can add them easily yourself without using TwigBridge.

        /*
         * Register markup tags
         */
        MarkupManager::instance()->registerCallback(function($manager){
            $manager->registerFunctions([
                // Functions
                'post'           => 'post',
                'link_to'        => 'link_to',
                'link_to_asset'  => 'link_to_asset',
                'link_to_route'  => 'link_to_route',
                'link_to_action' => 'link_to_action',
                'asset'          => 'asset',
                'action'         => 'action',
                'url'            => 'url',
                'route'          => 'route',
                'secure_url'     => 'secure_url',
                'secure_asset'   => 'secure_asset',

                // Classes
                'str_*'          => ['Str', '*'],
                'url_*'          => ['URL', '*'],
                'html_*'         => ['HTML', '*'],
                'form_*'         => ['Form', '*'],
                'form_macro'     => ['Form', '__call'],
            ]);

            $manager->registerFilters([
                // Classes
                'slug'           => ['Str', 'slug'],
                'plural'         => ['Str', 'plural'],
                'singular'       => ['Str', 'singular'],
                'finish'         => ['Str', 'finish'],
                'snake'          => ['Str', 'snake'],
                'camel'          => ['Str', 'camel'],
                'studly'         => ['Str', 'studly'],
                'md'             => ['October\Rain\Support\Markdown', 'parse'],
            ]);
        });