JabRef should be able to parse Citation File Format (CFF) and export into it.
Information about the format can be found here.

https://citation-file-format.github.io/
See also https://github.com/citation-file-format/cff-converter-python

Implementation details.
Look at other importers, org.jabref.logic.importer
For YAML parsing, JabRef includes already the jackson yaml parser
https://github.com/FasterXML/jackson-dataformats-text/tree/2.13/yaml