composer create-project drupal-composer/drupal-project:8.x-dev

composer require/admin_toolbar

$ composer require drupal/admin_toolbar

Using version ^1.24 for drupal/admin_toolbar
./composer.json has been updated
> DrupalProjectcomposerScriptHandler::checkComposerVersion
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 42 installs, 0 updates, 0 removals
  - Installing drupal/admin_toolbar (1.24.0): Downloading (100%)
  - Installing symfony/phpunit-bridge (v3.4.18): Downloading (100%)
  - Installing sebastian/recursion-context (3.0.0): Downloading (100%)
  - Installing sebastian/exporter (3.1.0): Downloading (100%)
  - Installing sebastian/diff (2.0.1): Downloading (100%)
  - Installing sebastian/comparator (2.1.3): Downloading (100%)
  - Installing phpdocumentor/reflection-common (1.0.1): Downloading (100%)
  - Installing phpdocumentor/type-resolver (0.4.0): Downloading (100%)
  - Installing phpdocumentor/reflection-docblock (4.3.0): Downloading (100%)
  - Installing doctrine/instantiator (1.1.0): Downloading (100%)
  - Installing phpspec/prophecy (1.8.0): Downloading (100%)
  - Installing sebastian/version (2.0.1): Downloading (100%)
  - Installing sebastian/resource-operations (1.0.0): Downloading (100%)
  - Installing sebastian/object-reflector (1.1.1): Downloading (100%)
  - Installing sebastian/object-enumerator (3.0.3): Downloading (100%)
  - Installing sebastian/global-state (2.0.0): Downloading (100%)
  - Installing sebastian/environment (3.1.0): Downloading (100%)
  - Installing phpunit/php-text-template (1.2.1): Downloading (100%)
  - Installing phpunit/phpunit-mock-objects (5.0.10): Downloading (100%)
  - Installing phpunit/php-timer (1.0.9): Downloading (100%)
  - Installing phpunit/php-file-iterator (1.4.5): Downloading (100%)
  - Installing theseer/tokenizer (1.1.0): Downloading (100%)
  - Installing sebastian/code-unit-reverse-lookup (1.0.1): Downloading (100%)
  - Installing phpunit/php-token-stream (2.0.2): Downloading (100%)
  - Installing phpunit/php-code-coverage (5.3.2): Downloading (100%)
  - Installing phar-io/version (1.0.1): Downloading (100%)
  - Installing phar-io/manifest (1.0.1): Downloading (100%)
  - Installing myclabs/deep-copy (1.8.1): Downloading (100%)
  - Installing phpunit/phpunit (6.5.13): Downloading (100%)
  - Installing mikey179/vfsstream (v1.6.5): Downloading (100%)
  - Installing jcalderonzumba/gastonjs (v1.2.0): Downloading (100%)
  - Installing behat/mink (dev-master d5ee350): Cloning d5ee350c40 from cache
  - Installing jcalderonzumba/mink-phantomjs-driver (v0.3.3): Downloading (100%)
  - Installing squizlabs/php_codesniffer (3.3.2): Downloading (100%)
  - Installing drupal/coder (8.3.1): Cloning 29a25627e7 from cache
  - Installing instaclick/php-webdriver (1.4.5): Downloading (100%)
  - Installing behat/mink-selenium2-driver (dev-master 8684ee4): Cloning 8684ee4e63 from cache
  - Installing symfony/browser-kit (v4.1.7): Downloading (100%)
  - Installing fabpot/goutte (v3.2.3): Downloading (100%)
  - Installing behat/mink-browserkit-driver (1.3.3): Downloading (100%)
  - Installing behat/mink-goutte-driver (v1.2.1): Downloading (100%)
sebastian/global-state suggests installing ext-uopz (*)
phpunit/phpunit-mock-objects suggests installing ext-soap (*)
phpunit/phpunit suggests installing phpunit/php-invoker (^1.1)
behat/mink suggests installing behat/mink-zombie-driver (fast and JS-enabled headless driver for any app (requires node.js))
behat/mink suggests installing dmore/chrome-mink-driver (fast and JS-enabled driver for any app (requires chromium or google chrome))
Writing lock file
Generating autoload files
> DrupalProjectcomposerScriptHandler::createRequiredFiles