Horde system user authentication (ServiceAccounts)

We are using Horde for distributed compilation for our developers and have configured Horde with Okta SSO.
We would like to also allow our current CI system, which runs on TeamCity, to utilize Horde agents for compilation, but these agents can obviously not perform a SSO login.
Is there a way to handle this situation?

I see that Horde has the concept of ServiceAccounts, but there’s no documentation of what they are used for or how to use them.
I have created a ServiceAccount, which provides me with an id and a token, but I don’t seem to be able to use it for anything when the auth provider is set to OIDC/Okta.
Attempting to log in (/account/login/horde) and get a token for BuildConfiguration.xml results in a somewhat buggy error message:

Unhandled exception: No authentication handler is registered for the scheme ‘Horde built-in authentication is disabled’. The registered schemes are: Cookies, ServiceAccount, OktaOpenIdConnect, ServerJwt, ExternalJwt.

Should I be able to use ServiceAccounts for this scenario and if so, what do I need to configure or do to authenticate?