An example of how to access apollo context in formatError() method.

CustomApolloServer.ts

import { Request, Response } from "express";
import { GraphQLError, GraphQLFormattedError } from "graphql";
import { GraphQLServerOptions } from "apollo-server-core/src/graphqlOptions";
import { ApolloServer, ApolloServerExpressConfig as C } from "apollo-server-express";

export type FormatError = (graphQLError: GraphQLError, context: unknown) => GraphQLFormattedError;

export type ApolloServerExpressConfig = Omit<C, "formatError"> & {
  formatError?: FormatError;
};

/**
 * A modified instance of apollo express server class
 * that calls formatError() method with the context value.
 */
export class CustomApolloServer extends ApolloServer {
  constructor(config: ApolloServerExpressConfig) {
    super(config as C);
  }

  async createGraphQLServerOptions(req: Request, res: Response): Promise<GraphQLServerOptions> {
    const options = await super.createGraphQLServerOptions(req, res);

    if (typeof options.formatError === "function") {
      const formatError = options.formatError as FormatError;

      // eslint-disable-next-line @typescript-eslint/ban-ts-comment
      // @ts-ignore
      options.formatError = (graphQLError: GraphQLError) => {
        return formatError(graphQLError, options.context);
      };
    }

    return options;
  }
}