Finding mutual friends on facebook

Question

I want to find out mutual friends between two random users using the facebook Graph API v2.2.

I read through the documentation https://developers.facebook.com/docs/graph

Answer 1

I am about to implement this myself. I have a similar use case where the two users may not be friends but I'd like to see which of their friends are mutual.

Apparently, you have to include an 'app proof' parameter with the API request from your server when the two users are not mutual friends:

If you want to call this endpoint on behalf two app-users who are not friends, then you must provide the appsecret_proof parameter along with the user access token when making the request. This means you must call this endpoint from your server.

Looks like this might be a good idea to do anyway.