No package mod_auth_external available.

This error message suggests that the mod_auth_external package is not installed on your system.

You can try installing it using your system's package manager. For example, on a Debian-based system, you can run the following command in the terminal:

sudo apt-get install libapache2-mod-authnz-external

On a Red Hat-based system, you can run:

sudo yum install mod_auth_external

After installing the package, you may need to enable the module in Apache's configuration file. You can do this by adding the following line to the file:

LoadModule authnz_external_module /usr/lib/apache2/modules/mod_authnz_external.so

Finally, restart Apache to apply the changes:

sudo systemctl restart apache2

I hope this helps!