Enable the Puppet Core repositories on Apt

Download the package and run the dpkg tool in install mode:
```
wget --content-disposition <package_URL>
sudo dpkg -i <file_name>.deb
```

For example, to enable the Ubuntu focal repository:

wget --content-disposition https://apt-puppetcore.puppet.com/public/puppet8-release-focal.deb
sudo dpkg -i puppet8-release-focal.deb

Edit the /etc/apt/auth.conf.d/<file_name>.conf file to add the credentials:

#login forge-key
#password <API_KEY>

forge-key is a string literal.

See the following example.

$ sudo vi /etc/apt/auth.conf.d/apt-puppetcore-puppet.conf
machine apt-puppetcore.puppet.com
login forge-key
password <API_KEY>

Update the apt package lists:
```
sudo apt-get update
```

Results Certain operating systems and installation methods automatically verify package signatures. In these cases, you don’t need to do anything to verify the package signature. These methods include:

If you install from the Puppet Yum and Apt repositories, the release package that enables the repository also installs our release signing key. The Yum and Apt tools automatically verify the integrity of packages as you install them.
If you install a Windows agent using an .msi package, the Windows installer automatically verifies the signature before installing the package.
If you need to manually verify packages, see Verify packages.
If you install a .dmg package on macOS, the installer automatically verifies the signature before installing the package.