WIP: docs: added docs for x509/mtls

[igpetrov]

Description

docs: added docs for x509/mtls

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[github-actions]

👋 🤖 🤔 Hello, @igpetrov! Did you make your changes in all the right places?

These files were changed only in versioned_docs/version-8.6/. You might want to duplicate these changes in docs/.

• versioned_docs/version-8.6/self-managed/operational-guides/using-x509-authorizers.md

You may have done this intentionally, but we wanted to point it out in case you didn't. You can read more about the versioning within our docs in our documentation guidelines.

[akeller]

@igpetrov can you link to info about this PR? Is this part of the upcoming alpha or something else? I want to make sure we can get a tech writer to review it when you are ready 🙂

[igpetrov]

Hi @akeller

Sorry for low context. It was last-minute request before my FTO with intention "this is better then nothing" to unblock one of our customers. The context in this channel starting from the message and all below: https://camunda.slack.com/archives/C07DMDRTSQJ/p1734534541809249.

Long story short: there is a X509 authorizers feature. Old architecture (pre-8.7) and new architecture (8.7) have two different implementations. This PR is for the old one, but only for 8.6. Versions below 8.6 are not supported.

Since I am back this week, I planned to polish this PR in the upcoming days.