Codigo que atualizar o composer.json e instala o novo compoente atraves de uma pagina em php

install_a_component_by_composer.php

<?php
// componentes requeridos
// composer/composer
// symfony/console

// classes requeridas
// use Composer\Command\UpdateCommand;
// use Symfony\Component\Console\Input\ArrayInput;
// use Composer\Console\Application;


       //roda o composer para baixar e instalar a dependencia. Antes add-la ao composer.json
	
       $output = new \Symfony\Component\Console\Output\ConsoleOutput();

       $application = new Application();

       $input = new ArrayInput(array(
           'command' => 'update'
       ));
        
       $application->setAutoExit(false);

       $application->run($input,$output);
        
        
       //atualiza o composer para add o componente requerido
        
       $filename = realpath(__DIR__.'/../../../../../').'/composer.json';
       $jsonfile = file_get_contents($filename);
       echo '<pre>';
       $file =  json_decode($jsonfile);
       $arr = new \ArrayObject($file->require);
       $ar = $arr->getArrayCopy();
       $ar["monolog/monolog"] =  "~1.11";
       $file->require = $ar;
       file_put_contents($filename, str_replace('\\','',json_encode($file)));