Our consultant Florencia Vitale solved the question!
GAS doesn't has an specific configuration to force HTTPS, and the RewriteRule on the .htaccess file has no effect on Genero sites.
So you have to place the RewriteRule bellow at the Apache's httpd.conf file:
<VirtualHost [SERVER IP]:80>
RewriteEngine On
# Rewrite all GAS applications to SSL
RewriteCond %{REQUEST_URI} ^/gas
RewriteRule (.*) https://[YOUR DOMAIN]/$1 [L,R,QSA]
</VirtualHost>