Composer Warning: openssl extension is missing. How to enable in WAMP

In addition to uncommenting the ;extension=php_openssl.dll line in php.ini that everyone else has mentioned, you also have to ensure the ;extension_dir = "ext" line is also uncommented. To uncomment, remove the prefixed semicolon and save.

That line might already be uncommented in packages like WAMP and XAMPP, but it's not in a plain PHP download for Windows, so it's worth verifying. Also, you have to create the php.ini file by copying one of the examples, like php.ini-development to a new file and then name it php.ini. Then make these changes there.

Also, in the future, to install tools such as PHP and Composer, I recommend using the Chocolatey package manager. Then it's as simple as choco install composer. Of course, you'd still need to edit php.ini before installing Composer with the choco method. In future versions of Windows, package management tools like Chocolatey will be baked into Windows, the same way apt-get is in Ubuntu. Exciting times ahead for developers!

With either method, after installing Composer, don't forget to restart your terminal. Whether you're using Command Prompt, Bash (installs with Git), or Powershell, you'll need to restart it before the updated environmental variables work.

WAMP uses different php.ini files in the CLI and for Apache. when you enable php_openssl through the WAMP UI, you enable it for Apache, not for the CLI. You need to modify C:\wamp\bin\php\php-5.4.3\php.ini to enable it for the CLI.