A lot of buttons on Sign up page

We're planning to redesign the signup procedures on our landing page at my company. We want to add options for users to register with their credentials or using OAuth buttons. The problem is a big quantity (about 20) of these buttons.

I think that it is a bad idea to add a lot of buttons. The 3-4 popular systems are enough.

My question is: Is there any study about big quantity of sign up buttons? Is there any other examples of using this kind of sign up pages?