URQL + Firebase authentication

urqlClient.ts

import {
  Exchange,
  cacheExchange,
  createClient,
  dedupExchange,
  fetchExchange,
  subscriptionExchange,
} from 'urql'
import { delay, empty, fromPromise, map, mergeMap, pipe, tap } from 'wonka'
import firebase from 'firebase' // NOTE: This is old Firebase version

const headerExchange: Exchange = ({ forward }) => (operations$) =>
  pipe(
    operations$,
    mergeMap((operation) => {
      const currentUser = firebase.auth().currentUser
      if (!currentUser) {
        return pipe(
          empty,
          map(() => operation),
        )
      }
      return pipe(
        fromPromise(currentUser.getIdToken()),
        map((authToken) => {
          if (!operation.context.fetchOptions) {
            operation.context.fetchOptions = {}
          }
          Object.assign(operation.context.fetchOptions, {
            headers: {
              accept: 'application/json',
              Authorization: `Bearer ${authToken}`,
            },
          })
          return operation
        }),
      )
    }),
    forward,
  )