WordPress generally gives you page to fill FTP connection details when you try to install new plugin or update wordpress. The reason is it cannot write to wp-content directory due of lack of permissions to write. The best way is to change permissions and ownership of wp-content directory. But if you can’t do that because of some reason, then add the below line of code in your wp-config.php

define(‘FS_METHOD’, ‘direct’);

Other way is to change permissions and ownerships to wp-content directory as said.

 chown -R www-data wordpress  
chgrp -R www-data wordpress  
chmod -R 755 wordpress/wp-content