Documentation and up-to-date example for authorization and encryption for client missing

[aliksimon]

Describe the bug

The function asyncua.crypto.cert_gen.setup_self_signed_certificate used in the example for client with encryption does not exist.

To Reproduce

Open python console, run:

import asyncua
help(asyncua.crypto.cert_gen.setup_self_signed_certificate)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'asyncua.crypto' has no attribute 'cert_gen'

help(asyncua.crypto)
Help on package asyncua.crypto in asyncua:

NAME
    asyncua.crypto

PACKAGE CONTENTS
    cert_gen
    permission_rules
    security_policies
[...]

Expected behavior

A docstring a shown instead an AttributeError.

Or rather: the function is not used in the example and instead existing functions are used.

Version

Python-Version: 3.10.19

opcua-asyncio Version: 1.1.8

The actual problem:
There is no documentation about how to use certificates to ensure:

• the client knows that the server is who it claims (authentification)
• the server knows that the client is who it claims and is allowed to read (authentification)
• the data transferred is encrypted

I would expect documentation here: https://opcua-asyncio.readthedocs.io/en/latest/api/asyncua.crypto.html but the page is basically empty, and here https://opcua-asyncio.readthedocs.io/en/latest/usage/client/overview.html but it's a todo.

If I understand it (with your help probably) I can also contribute a PR for the docs.