headless on craft cms is pretty new. It took me some time passing the preview token and making the whole roundtrip through the nextjs params > apollo auth > graphql.
I made a gist for the apollo.js config

import React from 'react'
import Head from 'next/head'
import { ApolloProvider } from '@apollo/react-hooks'
import { ApolloClient } from 'apollo-client'
import { InMemoryCache, IntrospectionFragmentMatcher } from 'apollo-cache-inmemory'
import { createHttpLink } from 'apollo-link-http';
import { setContext } from 'apollo-link-context';
import fetch from 'isomorphic-unfetch'
import introspectionQueryResultData from '../fragmentTypes.json'
import querystring from 'querystring'

let apolloClient = null

const fragmentMatcher = new IntrospectionFragmentMatcher({
  introspectionQueryResultData
});

/**
 * Creates and provides the apolloContext
 * to a next.js PageTree. Use it by wrapping
 * your PageComponent via HOC pattern.
 * @param {Function|Class} PageComponent
 * @param {Object} [config]
 * @param {Boolean} [config.ssr=true]
 */
export function withApollo(PageComponent, { ssr = true } = {}) {
  const WithApollo = ({ apolloClient, apolloState, ...pageProps }) => {
    const token = pageProps.router.query.token
    const client = apolloClient || initApolloClient({ ...apolloState, token })
    return (
      
        
      
    )
  }

  // Set the correct displayName in development
  if (process.env.NODE_ENV !== 'production') {
    const displayName =
      PageComponent.displayName || PageComponent.name || 'Component'

    if (displayName === 'App') {
      console.warn('This withApollo HOC only works with PageComponents.')
    }

    WithApollo.displayName = `withApollo(${displayName})`
  }

  if (ssr || PageComponent.getInitialProps) {
    WithApollo.getInitialProps = async ctx => {
      const { AppTree } = ctx

      const token = querystring.parse(ctx.req.url).token
      const apolloClient = (ctx.apolloClient = initApolloClient({ token }))

      // Run wrapped getInitialProps methods
      let pageProps = {}
      if (PageComponent.getInitialProps) {
        pageProps = await PageComponent.getInitialProps(ctx)
      }

      // Only on the server:
      if (typeof window === 'undefined') {
        // When redirecting, the response is finished.
        // No point in continuing to render
        if (ctx.res && ctx.res.finished) {
          return pageProps
        }

        // Only if ssr is enabled
        if (ssr) {
          try {
            // Run all GraphQL queries
            const { getDataFromTree } = await import('@apollo/react-ssr')
            await getDataFromTree(
              
            )
          } catch (error) {
            // Prevent Apollo Client GraphQL errors from crashing SSR.
            // Handle them in components via the data.error prop:
            // https://www.apollographql.com/docs/react/api/react-apollo.html#graphql-query-data-error
            console.error('Error while running `getDataFromTree`', error)
          }

          // getDataFromTree does not call componentWillUnmount
          // head side effect therefore need to be cleared manually
          Head.rewind()
        }
      }

      // Extract query data from the Apollo store
      const apolloState = apolloClient.cache.extract()

      return {
        ...pageProps,
        apolloState
      }
    }
  }

  return WithApollo
}

/**
 * Always creates a new apollo client on the server
 * Creates or reuses apollo client in the browser.
 * @param  {Object} initialState
 */
function initApolloClient(initialState) {
  // Make sure to create a new client for every server-side request so that data
  // isn't shared between connections (which would be bad)
  if (typeof window === 'undefined') {
    return createApolloClient(initialState)
  }

  // Reuse client on the client-side
  if (!apolloClient) {
    apolloClient = createApolloClient(initialState)
  }

  return apolloClient
}

/**
 * Creates and configures the ApolloClient
 * @param  {Object} [initialState={}]
 */
function createApolloClient(initialState = {}) {
  const token = initialState.token
  const uri = `${process.env.CRAFT_GQL_URL}${token !== undefined ? `?token=${token}` : ''}`

  const httpLink = createHttpLink({
    uri,
    fetch
  });

  const authLink = setContext((request, { headers }) => {
    return {
      headers: {
        ...headers
        // authorization: process.env.CRAFT_GQL_TOKEN
        // authorization: token ? `Bearer ${token}` : ''
      }
    }
  });

  // Check out https://github.com/zeit/next.js/pull/4611 if you want to use the AWSAppSyncClient
  return new ApolloClient({
    ssrMode: typeof window === 'undefined', // Disables forceFetch on the server (so queries are only run once)
    link: authLink.concat(httpLink),
    cache: new InMemoryCache({ fragmentMatcher }).restore(initialState)
  })
}
craftcms nextjs live preview
