Composer Autoload in CodeIgniter. This method provides Cmposer autoloader to be loaded before CodeIgniter classes. Useful to be used with dotenv file using PHP Dotenv package by josegonzalez.

index.php

<?php
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2015, British Columbia Institute of Technology
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @package CodeIgniter
 * @author  EllisLab Dev Team
 * @copyright   Copyright (c) 2008 - 2014, EllisLab, Inc. (http://ellislab.com/)
 * @copyright   Copyright (c) 2014 - 2015, British Columbia Institute of Technology (http://bcit.ca/)
 * @license http://opensource.org/licenses/MIT  MIT License
 * @link    http://codeigniter.com
 * @since   Version 1.0.0
 * @filesource
 */

/*
 *---------------------------------------------------------------
 * SET DEFAULT TIMEZONE
 *---------------------------------------------------------------
 *
 * The DateTime class depends on default timezone setting. Unfortunately,
 * we were unable to set it using $config['time_reference'] in
 * application/config/config.php. So we have to do it manually here using
 * date_default_timezone_set(). Default to Asia/Jakarta (GMT+7 or WIB)
 */
	date_default_timezone_set('Asia/Jakarta');

/*
 *---------------------------------------------------------------
 * COMPOSER AUTO-LOADING
 *---------------------------------------------------------------
 *
 * Using this method, you don't need to set $config['composer_autoload']
 * to TRUE in application/config/config.php. Also, all packages installed
 * using Composer will be loaded immediately BEFORE any CodeIgniter classes
 */
	require '../vendor/autoload.php';

/*
 *---------------------------------------------------------------
 * LOAD DOTENV FILE
 *---------------------------------------------------------------
 *
 * Load enviroment variables from .env file
 *
 * Make sure .env is located in root and containing these variables:
 *
 *     STATE : will be used asapplication environment
 *     DB_*  : It's obvious, the database configurations
 */
	josegonzalez\Dotenv\Loader::load(array(
		'filepath' => str_replace('public', '.env', __DIR__),
		'expect' => array(
			'STATE',
			'DB_HOST',
			'DB_NAME',
			'DB_USER',
			'DB_PASS',
		),
		'toEnv' => true
	));

/*
 *---------------------------------------------------------------
 * APPLICATION ENVIRONMENT
 *---------------------------------------------------------------
 *
 * You can load different configurations depending on your
 * current environment. Setting the environment also influences
 * things like logging and error reporting.
 *
 * This can be set to anything, but default usage is:
 *
 *     development
 *     testing
 *     production
 *
 * NOTE: If you change these, also change the error_reporting() code below
 */
	define('ENVIRONMENT', $_ENV['STATE']);

/*
 *---------------------------------------------------------------
 * ERROR REPORTING
 *---------------------------------------------------------------
 *
 * Different environments will require different levels of error reporting.
 * By default development will show errors but testing and live will hide them.
 */
switch (ENVIRONMENT)
{
	case 'development':
		error_reporting(-1);
		ini_set('display_errors', 1);
	break;

	case 'testing':
	case 'production':
		ini_set('display_errors', 0);
		if (version_compare(PHP_VERSION, '5.3', '>='))
		{
			error_reporting(E_ALL & ~E_NOTICE & ~E_DEPRECATED & ~E_STRICT & ~E_USER_NOTICE & ~E_USER_DEPRECATED);
		}
		else
		{
			error_reporting(E_ALL & ~E_NOTICE & ~E_STRICT & ~E_USER_NOTICE);
		}
	break;

	default:
		header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
		echo 'The application environment is not set correctly.';
		exit(1); // EXIT_ERROR
}

/*
 *---------------------------------------------------------------
 * SYSTEM FOLDER NAME
 *---------------------------------------------------------------
 *
 * This variable must contain the name of your "system" folder.
 * Include the path if the folder is not in the same directory
 * as this file.
 */
	$system_path = '../system';

/*
 *---------------------------------------------------------------
 * APPLICATION FOLDER NAME
 *---------------------------------------------------------------
 *
 * If you want this front controller to use a different "application"
 * folder than the default one you can set its name here. The folder
 * can also be renamed or relocated anywhere on your server. If
 * you do, use a full server path. For more info please see the user guide:
 * http://codeigniter.com/user_guide/general/managing_apps.html
 *
 * NO TRAILING SLASH!
 */
	$application_folder = '../app';

/*
 *---------------------------------------------------------------
 * VIEW FOLDER NAME
 *---------------------------------------------------------------
 *
 * If you want to move the view folder out of the application
 * folder set the path to the folder here. The folder can be renamed
 * and relocated anywhere on your server. If blank, it will default
 * to the standard location inside your application folder. If you
 * do move this, use the full server path to this folder.
 *
 * NO TRAILING SLASH!
 */
	$view_folder = '';


/*
 * --------------------------------------------------------------------
 * DEFAULT CONTROLLER
 * --------------------------------------------------------------------
 *
 * Normally you will set your default controller in the routes.php file.
 * You can, however, force a custom routing by hard-coding a
 * specific controller class/function here. For most applications, you
 * WILL NOT set your routing here, but it's an option for those
 * special instances where you might want to override the standard
 * routing in a specific front controller that shares a common CI installation.
 *
 * IMPORTANT: If you set the routing here, NO OTHER controller will be
 * callable. In essence, this preference limits your application to ONE
 * specific controller. Leave the function name blank if you need
 * to call functions dynamically via the URI.
 *
 * Un-comment the $routing array below to use this feature
 */
	// The directory name, relative to the "controllers" folder.  Leave blank
	// if your controller is not in a sub-folder within the "controllers" folder
	// $routing['directory'] = '';

	// The controller class file name.  Example:  mycontroller
	// $routing['controller'] = '';

	// The controller function you wish to be called.
	// $routing['function'] = '';


/*
 * -------------------------------------------------------------------
 *  CUSTOM CONFIG VALUES
 * -------------------------------------------------------------------
 *
 * The $assign_to_config array below will be passed dynamically to the
 * config class when initialized. This allows you to set custom config
 * items or override any default config values found in the config.php file.
 * This can be handy as it permits you to share one application between
 * multiple front controller files, with each file containing different
 * config values.
 *
 * Un-comment the $assign_to_config array below to use this feature
 */
	// $assign_to_config['name_of_config_item'] = 'value of config item';



// --------------------------------------------------------------------
// END OF USER CONFIGURABLE SETTINGS.  DO NOT EDIT BELOW THIS LINE
// --------------------------------------------------------------------

/*
 * ---------------------------------------------------------------
 *  Resolve the system path for increased reliability
 * ---------------------------------------------------------------
 */

	// Set the current directory correctly for CLI requests
	if (defined('STDIN'))
	{
		chdir(dirname(__FILE__));
	}

	if (($_temp = realpath($system_path)) !== FALSE)
	{
		$system_path = $_temp.'/';
	}
	else
	{
		// Ensure there's a trailing slash
		$system_path = rtrim($system_path, '/').'/';
	}

	// Is the system path correct?
	if ( ! is_dir($system_path))
	{
		header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
		echo 'Your system folder path does not appear to be set correctly. Please open the following file and correct this: '.pathinfo(__FILE__, PATHINFO_BASENAME);
		exit(3); // EXIT_CONFIG
	}

/*
 * -------------------------------------------------------------------
 *  Now that we know the path, set the main path constants
 * -------------------------------------------------------------------
 */
	// The name of THIS file
	define('SELF', pathinfo(__FILE__, PATHINFO_BASENAME));

	// Path to the system folder
	define('BASEPATH', str_replace('\\', '/', $system_path));

	// Path to the front controller (this file)
	define('FCPATH', str_replace(SELF, '', __FILE__));

	// Name of the "system folder"
	define('SYSDIR', trim(strrchr(trim(BASEPATH, '/'), '/'), '/'));

	// The path to the "application" folder
	if (is_dir($application_folder))
	{
		if (($_temp = realpath($application_folder)) !== FALSE)
		{
			$application_folder = $_temp;
		}

		define('APPPATH', $application_folder.DIRECTORY_SEPARATOR);
	}
	else
	{
		if ( ! is_dir(BASEPATH.$application_folder.DIRECTORY_SEPARATOR))
		{
			header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
			echo 'Your application folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF;
			exit(3); // EXIT_CONFIG
		}

		define('APPPATH', BASEPATH.$application_folder.DIRECTORY_SEPARATOR);
	}

	// The path to the "views" folder
	if ( ! is_dir($view_folder))
	{
		if ( ! empty($view_folder) && is_dir(APPPATH.$view_folder.DIRECTORY_SEPARATOR))
		{
			$view_folder = APPPATH.$view_folder;
		}
		elseif ( ! is_dir(APPPATH.'views'.DIRECTORY_SEPARATOR))
		{
			header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
			echo 'Your view folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF;
			exit(3); // EXIT_CONFIG
		}
		else
		{
			$view_folder = APPPATH.'views';
		}
	}

	if (($_temp = realpath($view_folder)) !== FALSE)
	{
		$view_folder = $_temp.DIRECTORY_SEPARATOR;
	}
	else
	{
		$view_folder = rtrim($view_folder, '/\\').DIRECTORY_SEPARATOR;
	}

	define('VIEWPATH', $view_folder);

/*
 * --------------------------------------------------------------------
 * LOAD THE BOOTSTRAP FILE
 * --------------------------------------------------------------------
 *
 * And away we go...
 */
require_once BASEPATH.'core/CodeIgniter.php';