Install mod_setenvifplus for Apache2

As root or sudo:

# aptitude install apache2-dev libssl-dev

Compile and install:

# wget https://sourceforge.net/projects/modsetenvifplus/files/latest/download
# tar zxvf ./mod_setenvifplus-0.40-src.tar.gz
# cd mod_setenvifplus-0.40
# apxs -i -c mod_setenvifplus.c -lcrypto

The module is created in:

/usr/lib/apache2/modules/mod_setenvifplus.so

Manually create load file in Apache conf:

/etc/apache2/mods-available/setenvifplus.load:
LoadModule setenvifplus_module /usr/lib/apache2/modules/mod_setenvifplus.so

Enable module:

# a2enmod setenvifplus

Check if the module is installed:

# apachectl -M | grep setenvifplus

1. https://sourceforge.net/projects/modsetenvifplus/
2. mod_setenvifplus
3. apxs – APache eXtenSion tool