Configure Apache HTTP client in Java External Task Client

[ThorbenLindhauer]

This issue was imported from JIRA:

| Field | Value | | ---------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | JIRA Link | [CAM-12233](https://jira.camunda.com/browse/CAM-12233) | | Reporter | NYBzR2x

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User Story (Required on creation):

I can configure a socket timeout at the external task's httpClient, so once the timeout is reached an exception gets thrown and therefore the thread gets freed and the external task client continues operation (while logging the corresponding exception).

Functional Requirements (Required before implementation):

• There is a documented way how to change the socket timeout for all HTTP requests that the external task client makes

Technical Requirements (Required before implementation):

• Extend our client builder with a method that gives access to the internal Apache HttpClientBuilder instance.
• Update Apache HttpClient to version 5.

Limitations of Scope (Optional):

• The external task client generally doesn't fall into our public API guarantees (https://docs.camunda.org/manual/7.14/introduction/public-api/). Especially, the Apache-specific part of the new feature can be subject to change if we update the Apache HttpClient or in case we ever choose to switch to a different http client library

Hints (Optional):

• See also the discussion in https://github.com/camunda/camunda-external-task-client-java/pull/38
• External Task suddenly hung up - Camunda Platform 7 Topics / Camunda Platform 7 Process Engine - Camunda Platform Forum

Links

• is caused by https://jira.camunda.com/browse/SUPPORT-8263
• is related to https://jira.camunda.com/browse/CAMPLAN-9
• is related to https://jira.camunda.com/browse/SUPPORT-12742

Breakdown

### Pull Requests
- [ ] https://github.com/camunda/camunda-bpm-platform/issues/3944
- [ ] https://github.com/camunda/camunda-bpm-platform/issues/3945
- [ ] https://github.com/camunda/camunda-bpm-platform/issues/3946

Dev2QA handover

• [ ] Does this ticket need a QA test and the testing goals are not clear from the description? Add a Dev2QA handover comment

[tmetzke]

An additional option before we expose the internal HTTP client we use: Switch to the new Java HTTP Client and move the language level to Java 11.

Benefits:

• It allows for synchronous and asynchronous HTTP requests -> We could implement an asynchronous API (for complete, error, etc.) that client users could leverage. This brings the client closer to the Zeebe Client, simplifying a future migration to C8.
• It uses the HTTP 2 protocol by default and can switch back to HTTP 1.1 if the server doesn't support it. You can find a list of benefits of HTTP 2 over HERE.
• No additional HTTP client library is necessary anymore. Users can upgrade the HTTP client themselves by moving to a newer JDK. This should be way better regarding future maintenance (version updates, security issues, new features).
• The HTTP client also provides a builder that can be externalized so users can configure the client as they like.

Drawbacks:

• The HTTP request timeout is determined by the HTTP request, not by the client itself (as far as I can tell). This would imply that we also let users provide an HTTP request object for configuration. That "configuration" HTTP request can be used to build the actual HTTP requests via HttpRequest.newBuilder(HttpRequest request).
• We enforce a new JDK level (probably at least 11).
• Higher effort to replace the current client implementation.

[tasso94]

Note to DRI: @yanavasileva is interested in doing the review for this.

[yanavasileva]

Don't forget to adjust the version labels.

[danielkelemen]

Dev2QA

Run the Order Handling example, customize the HTTP Client using the new feature (add timeouts, proxies etc.) and verify that the client was initialized accordingly.