Calling AppSync from Lambda

index.js

const https = require('https');
const AWS = require("aws-sdk");
const urlParse = require("url").URL;
const appsyncUrl = process.env.API_BACKENDGRAPHQL_GRAPHQLAPIENDPOINTOUTPUT;
const region = process.env.REGION;
const endpoint = new urlParse(appsyncUrl).hostname.toString();
const graphqlQuery = require('./query.js').mutation;
const apiKey = process.env.API_KEY;

exports.handler = async (event) => {
    const req = new AWS.HttpRequest(appsyncUrl, region);

    const item = {
        input: {
            title: "Lambda Item",
            Content: "Item Generated from Lambda"
        }
    };

    req.method = "POST";
    req.headers.host = endpoint;
    req.headers["Content-Type"] = "application/json";
    req.body = JSON.stringify({
        query: graphqlQuery,
        operationName: "createLambdaGraphQL",
        variables: item
    });

    if (apiKey) {
        req.headers["x-api-key"] = apiKey;
    } else {
        const signer = new AWS.Signers.V4(req, "appsync", true);
        signer.addAuthorization(AWS.config.credentials, AWS.util.date.getDate());
    }

    const data = await new Promise((resolve, reject) => {
        const httpRequest = https.request({ ...req, host: endpoint }, (result) => {
            result.on('data', (data) => {
                resolve(JSON.parse(data.toString()));
            });
        });

        httpRequest.write(req.body);
        httpRequest.end();
    });

    return {
        statusCode: 200,
        body: data
    };
};

query.js

module.exports = {
    mutation: `mutation createLambdaGraphQL($input: CreateLambdaGraphQLInput!) {
      createLambdaGraphQL(input: $input) {
        id
        title
        Content
      }
    }
    `
}

Just FYI, this was taken from the official AWS Amplify docs here: https://docs.amplify.aws/cli/function#signing-a-request-from-lambda