CA_DIRECTORY_LAYOUTS

There are two basic (but orthogonal) aspect of directory-file layouts
used in tls-ca-manage.sh:

   - Layout: Traditional OpenSSL and New Centralized
   - Repo directory:  nested CA or single directory of CA directories

# Layout
The default OpenSSL directory layout (hereby called traditional) is
given below:

#  /etc/ssl ----> ca-root
#                   |
#                   +---> certs
#                   +---> private
#                   +---> newcerts
#                   +---> crl

The new centralized directory layout is:

# /etc -> ssl -+-> ca -+-> ca-root -+-> private
#              |                    +-> db
#              |
#              +-> etc
#              +-> certs
#              +-> crl

In conjunction with one of the layout above, the repo nesting is:

With traditional layout, nested CAs be like:

# /etc -> ssl -> ca-root -+-> ca-network    +-> TLS-server
#                         |                 +-> mail-server
#                         |                 +-> web-server
#                         |                 +-> SMTP-encryption
#                         +-> ca-component ---> timestamp-server
#                         +-> ca-identity  ---> employee-mail
#                         +-> ca-security  -+-> card-key
#                                           +-> guard-checkpoints

With centralized layout, nested CAs be like:

# /etc -> ssl -+-> ca -+-> ca-root -+-> private
#              |                    +-> db
#              |                    +-> ca-network +-> private
#              |                                   +-> db
#              |                                   +-> ca-mail +-> private
#              |                                               +-> db
#              +-> etc
#              +-> certs
#              +-> crl


Inspired by: https://pki-tutorial.readthedocs.io/en/latest/expert/index.html