Prune security concept page

[myidpt]

Today, the Istio security concept page is very long. We need to prune it to make it more crisp.

Specifically, the Authentication Policies and Authorization Policies sections are very long. We can shorten them by moving some content to security tasks.

[yangminzhu]

+1 to this, the concept page should really be shorter and mainly focus on explaining the high-level picture, architecture, important concepts and etc. Many of the detail description could and should be separated and moved to other places.

This helps new customers to quickly understand the most important concepts in Istio security and then they can choose to follow different docs for specific tasks.

Some ideas to get this started:

• Keep only the description of important concept in the Authentication policies and move the detail example either to the task page or the dedicated policy example page
• Keep only the description of important concept in the Authorization policies and move the detail example either to the task page or the dedicated policy example page
• Some contents can also be moved to the security best practices page
• Add tests for any of the new tasks or examples pages after the above steps
• Add some diagrams to better describe important mechanisms in the PeerAuthN, RequestAuthN and AuthZ API which is much better than describing in large amount of text. See example of the Authorization Policy Precedence diagram

@xulingqing You could first draft the actual changes in a doc and add oliver and me for a quicker review there, and later convert it to the actual PRs. Let me know if you have any questions and thanks again for taking this important work to improve the quality of our documentation.

[craigbox]

What about having "sub-concept" pages (@rcaballeromx was always keen on this) - we should not have pages that say "you will take 23 mins to read"!

[xulingqing]

Identity and Authn Part:

• PR: [Refactor] istio.io security concept page - Authn #10157
• Preview: https://deploy-preview-10157--preliminary-istio.netlify.app/latest/docs/concepts/security/

Authz Part:

• PR: [Refactor] istio.io security concept page - Authz #10164
• Preview: https://deploy-preview-10164--preliminary-istio.netlify.app/latest/docs/concepts/security/#authorization