The composer source will detect dependencies when php is available, a composer.lock file is found at an apps source_path, and a composer application file is found.
It enumerates dependencies and metadata by parsing composer.lock files for for dependency metadata and running php <composer application file> show --format json --path to obtain local dependency paths on disk.
The default composer application file location is <repository root>/composer.phar. To specify a custom composer file location, use the composer.application_path configuration setting.
composer:
application_path: "/path/to/composer"