Composer install error - requires ext_curl when it's actually enabled

This is caused because you don't have a library php5-curl installed in your system,

On Ubuntu its just simple run the line code below, in your case on Xamp take a look in Xamp documentation

sudo apt-get install php5-curl

For anyone who uses php7.0

sudo apt-get install php7.0-curl

For those who uses php7.1

sudo apt-get install php7.1-curl

For those who use php7.2

sudo apt-get install php7.2-curl

For those who use php7.3

sudo apt-get install php7.3-curl

For those who use php7.4

sudo apt-get install php7.4-curl

Or simply run below command to install by your version:

sudo apt-get install php-curl

This worked for me: http://ubuntuforums.org/showthread.php?t=1519176

After installing composer using the command curl -sS https://getcomposer.org/installer | php just run a sudo apt-get update then reinstall curl with sudo apt-get install php5-curl. Then composer's installation process should work so you can finally run php composer.phar install to get the dependencies listed in your composer.json file.

on php7 run for example:

> sudo apt-get install php-curl
> sudo apt-get install php-mbstring

for every missing extension. Then:

> sudo apt-get update

and finally (in the project's root folder):

> composer install