feat(gatsby-source-drupal): Provide proxyUrl in addition to baseUrl to allow using CDN, API gateway, etc.

packages/gatsby-source-drupal/README.md

@@ -250,6 +250,27 @@ module.exports = {
 }
 ```
 
+## CDN
+
+You can add an optional CDN or API gateway URL `proxyUrl` param. The URL can be a simple proxy of the Drupal
+`baseUrl`, or another URL (even containing a path) where the Drupal JSON API resources can be retrieved.
+
+```javascript
+// In your gatsby-config.js
+module.exports = {
+  plugins: [
+    {
+      resolve: `gatsby-source-drupal`,
+      options: {
+        baseUrl: `https://live-contentacms.pantheonsite.io/`,
+        proxyUrl: `https://xyz.cloudfront.net/`,
+        apiBase: `api`, // optional, defaults to `jsonapi`
+      },
+    },
+  ],
+}
+```
+
 ## GET Search Params
 
 You can append optional GET request params to the request url using `params` option.

packages/gatsby-source-drupal/src/gatsby-node.js

@@ -155,6 +155,7 @@ exports.sourceNodes = async (
   globalReporter = reporter
   const {
     baseUrl,
+    proxyUrl = baseUrl,
     apiBase = `jsonapi`,
     basicAuth = {},
     filters,
@@ -534,6 +535,11 @@ ${JSON.stringify(webhookBody, null, 4)}`
             }
           }
 
+          // If proxyUrl is defined, use it instead of baseUrl to get the content.
+          if (proxyUrl !== baseUrl) {
+            url = url.replace(baseUrl, proxyUrl)
+          }
+
           let d
           try {
             d = await requestQueue.push([
@@ -833,6 +839,9 @@ exports.pluginOptionsSchema = ({ Joi }) =>
     baseUrl: Joi.string()
       .required()
       .description(`The URL to root of your Drupal instance`),
+    proxyUrl: Joi.string().description(
+      `The CDN URL equivalent to your baseUrl`
+    ),
     apiBase: Joi.string().description(
       `The path to the root of the JSONAPI — defaults to "jsonapi"`
     ),