This answer is only for Linux(Ubuntu) users
++ Updated
There is default PHP installed as a system package but if you are using self contained installation of PHP (XAMPP [Binami]) then you have to provide php-config path in following attribute of ./configure command while installing the LIBSODIUM for your PHP.
--with-php-config
I have installed xampp-linux-x64-7.4.15-0 and surprisingly there is no sodium PHP module in this setup. I installed Sodium librarySodium library first and then install PHP Libsodium extesnion for XAMPP.
/opt/lampp/etc/php -m //Check if you have sodium installed
sudo apt-get update
sudo apt-get install build-essential libtool autoconf
Download stable version of Sodium Library by following link
https://github.com/jedisct1/libsodiumhttps://download.libsodium.org/libsodium/releases/ libsodium-1.x.x-stable.tar.gz
//Go inside the package folder
cd <downloaded package dir>
./configure
make
sudo make install
It will install library and you can check inside the /usr/local/lib/. The file for libsodium has been created with so extension.
Now we will download and install PHP library for
https://github.com/jedisct1/libsodium-php
//Go inside the package folder
cd <downloaded package dir>
phpize // This will create configure script.
./configure --with-php-config=/opt/lampp/bin/php-config //This time we provided preferred php config
make
sudo make install
This will isntall extension for XAMPP PHP and you can check sodium.so file has been created inside /opt/lampp7.4/lib/php/extensions/no-debug-non-zts-2019****.
Add extension inside php.ini
sudo bash -c 'echo "extension="sodium.so"" >> /opt/lampp/etc/php.ini'
Restart XAMPP and check installed php modules
sudo /opt/lampp/lampp restart
/opt/lampp/etc/php -m
If all works fine then you will find sodium in list defiantly.
CHEERS