Added Elasticsearch proxy example (#1398)

Co-authored-by: István Zoltán Szabó <istvan.szabo@elastic.co>

docs/examples/proxy/api/index.js

@@ -0,0 +1,76 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+// IMPORTANT: this is not a production ready code & purely for demonstration purposes,
+//            we make no guarantees on it's security and stability
+
+// NOTE: to make this endpoint work, you should create an ApiKey with 'write' permissions
+
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const authorize = require('../utils/authorize')
+
+const INDEX = '<index-name>'
+const client = new Client({
+  cloud: {
+    id: process.env.ELASTIC_CLOUD_ID
+  }
+})
+
+module.exports = async (req, res) => {
+  const [err, token] = authorize(req)
+  if (err) {
+    res.status(401)
+    res.json(err)
+    return
+  }
+
+  if (typeof req.body !== 'object') {
+    res.status(400)
+    res.json({
+      error: 'Bad Request',
+      message: 'The document should be an object',
+      statusCode: 400
+    })
+    return
+  }
+
+  try {
+    const response = await client.index({
+      index: INDEX,
+      id: req.query.id,
+      body: req.body
+    }, {
+      headers: {
+        Authorization: `ApiKey ${token}`
+      }
+    })
+
+    res.status(response.statusCode)
+    res.json(response.body)
+  } catch (err) {
+    res.status(err.statusCode || 500)
+    res.json({
+      error: err.name,
+      message: err.message,
+      statusCode: err.statusCode || 500
+    })
+  }
+}