Article 1, paragraph 2 of the United Nations charter allows for the right of self-determination.
- To develop friendly relations among nations based on respect for the principle of equal rights and self-determination of peoples, and to take other appropriate measures to strengthen universal peace;
The wikipedia article on self determination lists a number of issues around the definition of self-determination and its conflicts with territorial integrity, local constitutions and so on.
Practically today there are a number of secessionist movements such as Catalan, Scotland, Puerto Rico and Quebec. Are there any United Nations backed groups, or other international groups, working on dealing with the issues highlighted by these movements and the others listed on wikipedia and elsewhere to try to provide a structure or framework for peaceful expression of self-determination and secession from recognised sovereign states?
A full framing of rules for self-determination would also require addressing scenarios where a people wish to join another state. Real world examples would include Puerto Rico, Northern Ireland/RoI and topically (tongue in cheek) Greenland.