Federate existing GraphQL APIs

I wonder if it is possible to federate existing GraphQL endpoints into a NodeJS Apollo gateway ?

Actually we are using MongoDB ATLAS AppServices that allows us to expose our documents collections through a GraphQL API in few minutes. It’s really powerful. But, other teams in my company are also using this same technology and we are ended up with many independent graphQL endpoints. We are sharing some common entities and all those GraphQL APIs could be really good candidates for federation. But how?

Is it possible to put an Apollo Gateway in front of all those already existing endpoints and federate them ?

The Gql Schema of each of these endpoints is automatically generated and cannot be edited manually (to add some extra @keys for example). So, is federation possible just by adding an apollo gateway without touching these existing GraphQL apis ? Do you have an example to do this ?

Thank you for your help