I've noticed something interesting. Some of the leading Fascist (which is a far-right authoritarian ideology as you probably know) figures in Europe originated in Socialist/SocDem parties (Mussolini came from the Italian Socialist party and Mosley from the British Labour Party).
How and why did 2 people from Leftist parties become big figures in a Far-Right ideology?
I briefly touched on Mussolini's transition from socialist leader to fascism founder in this previous answer.
It's not exhaustive and it's a bit particular in its focus, but I hope it gives enough of a general picture to help you. Feel free to ask for clarification if some points remain obscure, of course.