docs: explain how to use java client with APIs in a c8run environment

[pepopowitz]

Description

This is follow-up to this discussion.

There is a trick to using the Java client to connect to APIs via cookie auth in a C8Run environment. Thanks to @tmetzke, this PR explains that trick.

It only applies to v8.6 and v8.7, as in v8.8 we no longer need cookie auth to connect to the APIs.'

When should this change go live?

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

PR Checklist

• My changes are for an upcoming minor release and:
  • are in the /docs directory (version 8.8).
  • are in the /versioned_docs/version-8.7/ directory (version 8.7).
• My changes are for an already released minor and are in a /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[github-actions]

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

These files were changed only in versioned_docs/version-8.7/. You might want to duplicate these changes in docs/.

• versioned_docs/version-8.7/apis-tools/camunda-api-rest/camunda-api-rest-authentication.md
• versioned_docs/version-8.7/self-managed/setup/deploy/local/c8run.md

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/apis-tools/camunda-api-rest/camunda-api-rest-authentication.md
• versioned_docs/version-8.6/self-managed/setup/deploy/local/c8run.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.

[conceptualshark]

This makes sense to me from a TW perspective - thank you for updating the C8Run page as well!

[tmetzke]

👍 Love it, great read! 🚀

💭 The C8Run instructions also mention the gRPC API. I am not the greatest expert in authentication mechanisms in our platform, but I believe that cookie authentication is not needed for that protocol. Maybe you can clarify this offline, and if this is indeed not needed, we should be clear about that in this C8Run guide. Currently, it somehow reads like it's necessary, but there is no example for gRPC calls, so that might confuse users at some point. This is non-blocking and can go into a follow-up.

[pepopowitz]

💭 The C8Run instructions also mention the gRPC API. I am not the greatest expert in authentication mechanisms in our platform, but I believe that cookie authentication is not needed for that protocol. Maybe you can clarify this offline, and if this is indeed not needed, we should be clear about that in this C8Run guide. Currently, it somehow reads like it's necessary, but there is no example for gRPC calls, so that might confuse users at some point. This is non-blocking and can go into a follow-up.

I don't personally have the capability to manage this follow-up right now.

[github-actions]

🧹 Preview environment for this PR has been torn down.