Show sample script

Signed-off-by: Michal Čihař <michal@cihar.com>
Better documentation for authentication modes

- move most of that to the setup section
- remove historical notes (like when it was introduced or originally
  called)
- include example scripts in the docs as well

Signed-off-by: Michal Čihař <michal@cihar.com>
Add crossreferences to the auth docs

Signed-off-by: Michal Čihař <michal@cihar.com>
Improve signon-script example

Signed-off-by: Michal Čihař <michal@cihar.com>