This summer the Slovenian parliament adopted a law that extends the responsibilities of the Slovenian regulator AGEN-RS to be issuing body for guarantees of origin for electricity, gas (including hydrogen) and heating and cooling. AGEN-RS has already many years of experience in issuing electricity GOs.
Act on the Promotion of the Use of Renewable Energy Sources in Slovenia: http://www.pisrs.si/Pis.web/pregledPredpisa?id=ZAKO8236