How to add user properties in Confluence?

[JIRA-Support ZKB]

Hi there

I am new with Confluence ScriptRunner, and I'm a bit lost. I have to create a screen, when a user connects to Confluence, where he has to accept the Conditions of use. 

I want to save the agreement as a user property, so I can later check who agreed and who didn't.

I couldn't find anything in Confluence about adding new properties/settings to the user.

Is there a way ? Did anybody do that ?

Thank you for your attention !

Pascal