From the SideFX folks:

The API is now in the beta phase and is open for testing from people outside of the company.

Here is a link to the API documentation:
https://www.sidefx.com/docs/api/download/index.html

Of interest are the "Generate credentials for API access" and "Download API" help pages.

So you should be able to start using the API for Houdini integration into the OpenVDB CI. Just keep in mind that it is still in beta so some things in the API may change.

I haven't decided where it is best to install this yet. At runtime or during image build. Let's investigate the runtime method first and move it to the image build if necessary.

If possible it would be good to remove the non-HDK components of the Houdini download after extracting the HDK.