How to invoke custom method in GraphQL::Schema

I am trying to add a check in GraphQL::Schema. I want to call a method where I have defined my schema. One Way is to call the method in GraphqlController. But, I am not able to get the arguments that are sent in the mutation/query only the query string. For example, I want custom validation across all mutations and queries.

class MySchema < GraphQL::Schema
  #my method to be called for each query/mutation
  mutation(Types::MutationType)
  query(Types::QueryType)
end