Composer_wrapper.php install failed!

What is needed to get the composer running?

Done:
su - librenms
./scripts/composer_wrapper.php install --no-dev

Result:
[[email protected]~]$ ./scripts/composer_wrapper.php install --no-dev
Error: Failed to download installer signature from https://composer.github.io/installer.sig
Composer not available, please manually install composer.

What are the Steps to install the composer manually when you are behind an proxy?

wget https://getcomposer.org/composer-stable.phar > Done to /opt/librenms/ as user librenms << right?
mv composer-stable.phar /usr/bin/composer > Directory /usr/bin/composer doesn`t exsist.
chmod +x /usr/bin/composer

Server:
Centos 8 new installed.