Manually sign AppSync URL to use in Lambda gives bad signature error

Question

In a Lambda, I would like to sign my AppSync endpoint with aws-signature-v4 in order to use it for a mutation.

The URL generated se

Answer 1

Adding an answer here because I had difficulty getting the accepted answer to work and I found an issue on the AWS SDK GitHub issues that said it's not recommended to use the AWS.Signers.V4 object in production. This is how I got it to work using the popular aws4 npm module that is recommended later on in the issue linked above.

const axios = require('axios');
const aws4 = require('aws4');

const query = `
    query Query {
      todos {
        id,
        title
      }
    }`

const sigOptions = {
        method: 'POST',
        host: 'xxxxxxxxxx.appsync-api.eu-west',
        region: 'eu-west-1',
        path: 'graphql',
        body: JSON.stringify({
            query
        }),
        service: 'appsync'
    };

const creds = {
    // AWS access tokens
}

axios({
        url: 'https://xxxxxxxxxx.appsync-api.eu-west/graphql',
        method: 'post',
        headers: aws4.sign(sigOptions, creds).headers,
        data: {
            query
        }
    }).then(res => res.data))