VICI (versatile IKE configuration protocol) is StrongSWAN's protocol for communicating with charon. See https://www.strongswan.org/apidoc/md_src_libcharon_plugins_vici_README.html

A Python module exists for it in the source tree even if it's not build by the Debian packaging and will have to be debianized separately.

The data formats are invonvenient at best, but it's still better than parsing a custom format.