There are two parts to this.
The actual htpasswd part, you could play even without OpenShift- Apache HTTPD can be configured to use the same kind of authentication files (in fact, htpasswd originates from Apache HTTPD), so you can practice adding/removing users from files with that.
But truly the full practice of configuring an identity provider in OpenShift and ussing the htpasswd one, you need a cluster where you can be an administrator. As far as I know, there are no free services online that do this (i.e. https://developers.redhat.com/developer-sandbox is a shared instance where you are not cluster admin).
ROL subscribers with access to courses such as DO280 (which matches EX280), can use the included lab environment, where they have cluster admin, to play with this. In fact, chapter 3 of the course has exercises related to this.
Another option as you mentioned is running your own cluster. The lowest cost option is CRC, which has been renamed to OpenShift Local:
https://developers.redhat.com/products/openshift-local/overview
That's a bit demanding on hardware resources, but apparently this is improving. The latest version requires 9gb of free RAM- previous versions I believe required more.
Kind regards,
Álex
