gatsby-node.js

const createNodeHelpers = require('gatsby-node-helpers').default;
const fetch = require('node-fetch');
const queryString = require('query-string');

const { createNodeFactory } = createNodeHelpers({
  typePrefix: `Marketo`
});

async function authenticate(authUrl) {
    const res = await fetch(authUrl, {});

    if (res.ok) {
      const {access_token} = await res.json();

      return access_token
    } else {
      throw new Error('Wrong credentials');
    }
}

exports.sourceNodes = async ({ actions }, configOptions) => {
  const { createNode } = actions;
  const { munchkinId, clientId, clientSecret, maxReturn } = configOptions;
  const authOptions = queryString.stringify({
    grant_type: 'client_credentials',
    client_id: clientId,
    client_secret: clientSecret
  });

  const formsApiUrl = `https://${munchkinId}.mktorest.com/rest/asset/v1/forms.json${maxReturn ? `?maxReturn=${maxReturn}` : ''}`;
  const authUrl = `https://${munchkinId}.mktorest.com/identity/oauth/token?${authOptions}`;

  try {
    const accessToken = await authenticate(authUrl);

    const forms = await fetch(formsApiUrl, {
      headers: { Authorization: `Bearer ${accessToken}` }
    }).then(res => res.json());

    async function fetchFormFields(id) {
      const url = `https://${munchkinId}.mktorest.com/rest/asset/v1/form/${id}/fields.json`;

      const results = await fetch(url, {
        headers: { Authorization: `Bearer ${accessToken}` }
      }).then(res => res.json());

      return results;
    };

    await Promise.all(
      forms.result.map(async form => {
        const {result: children} = await fetchFormFields(form.id);
        const Form = createNodeFactory('Form')({
          ...form,
          children
        });

        createNode(Form)
      })
    );
  } catch (err) {
    console.error("gatsby-source-marketo-forms:", err.message)
  }
}