Facetime

hello,I´ve been wanting to use imessage and facetime on my macbook air, but whenever i put my email and password i get a pop up from key chain trying to access my personal information stored. Which ever option i pick it resets of the log in page. I always clicked on Always Allow, Never allow or Allow and it redirects me onto that page. I have tried many methods but nothing works on my Mac but facetime and imessage works on my iphone perfectly Please help.🙂