This bug contains a hint of a feature request: https://github.com/linux-pam/linux-pam/issues/317#issuecomment-754088437 Namely, support a module argument that applies to "*" instead of requiring indirection through the default or a custom "config=<file>". This is not a use case I would have thought of, but it shouldn't be too hard to support.
Fixed with: https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=6926f78d99fc0e5ed5b10a06ffde79539b70df6a