This kind of person has a national authorization document, which means that the signature exercised by someone instead of the country is recognized by the country. Of course, the name of the authorization document will not be written as an authorization document, but will appear under other names, such as "Ambassador Extraordinary and Plenipotentiary of China to the United Nations". When an ambassador takes up his new post in the United Nations, he needs to submit a document to the United Nations office, stating that this person is a person sent by a certain country to represent the relevant country, his term of office and his rights. I remember that after Beijing's successful bid for the Olympic Games, it will sign a contract with the International Olympic Committee to host the Olympic Games. The authorization document issued by the government of China was handed over to the IOC before the representative signed it. During the Six-Party Talks in Beijing, negotiators from other countries need to submit to the Organizing Committee the document of "Extraordinary and Plenipotentiary Ambassador of a certain country to the Six-Party Talks in Beijing" issued by their own countries.