Manually sign AppSync URL to use in Lambda gives bad signature error - amazon-web-services

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 seems to be ok but it gives me the following error when I try it:
{
"errors" : [ {
"errorType" : "InvalidSignatureException",
"message" : "The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing method. Consult the service documentation for details. etc...
} ]
}
Here is my lambda function
import { Context, Callback } from 'aws-lambda';
import { GraphQLClient } from 'graphql-request';
const v4 = require('aws-signature-v4');
export async function handle(event: any, context: Context, callback: Callback) {
context.callbackWaitsForEmptyEventLoop = false;
const url = v4.createPresignedURL(
'POST',
'xxxxxxxxxxxxxxxxx.appsync-api.eu-west-1.amazonaws.com',
'/graphql',
'appsync',
'UNSIGNED-PAYLOAD',
{
key: 'yyyyyyyyyyyyyyyyyyyy',
secret: 'zzzzzzzzzzzzzzzzzzzzz',
region: 'eu-west-1'
}
);
const mutation = `{
FAKEviewProduct(title: "Inception") {
productId
}
}`;
const client = new GraphQLClient(url, {
headers: {
'Content-Type': 'application/graphql',
action: 'GetDataSource',
version: '2017-07-25'
}
});
try {
await client.request(mutation, { productId: 'jfsjfksldjfsdkjfsl' });
} catch (err) {
console.log(err);
callback(Error());
}
callback(null, {});
}
I got my key and secret by creating a new user and Allowing him appsync:GraphQL action.
What am I doing wrong?

Answer 1

This is how I trigger an AppSync mutation using by making a simple HTTP-request, using axios.
const AWS = require('aws-sdk');
const axios = require('axios');
exports.handler = async (event) => {
let result.data = await updateDb(event);
return result.data;
};
function updateDb({ owner, thingName, key }){
let req = new AWS.HttpRequest('https://xxxxxxxxxxx.appsync-api.eu-central-1.amazonaws.com/graphql', 'eu-central-1');
req.method = 'POST';
req.headers.host = 'xxxxxxxxxxx.appsync-api.eu-central-1.amazonaws.com';
req.headers['Content-Type'] = 'multipart/form-data';
req.body = JSON.stringify({
"query":"mutation ($input: UpdateUsersCamsInput!) { updateUsersCams(input: $input){ latestImage uid name } }",
"variables": {
"input": {
"uid": owner,
"name": thingName,
"latestImage": key
}
}
});
let signer = new AWS.Signers.V4(req, 'appsync', true);
signer.addAuthorization(AWS.config.credentials, AWS.util.date.getDate());
return axios({
method: 'post',
url: 'https://xxxxxxxxxxx.appsync-api.eu-central-1.amazonaws.com/graphql',
data: req.body,
headers: req.headers
});
}
Make sure to give the IAM-role your Lambda function is running as, permissions for appsync:GraphQL.

Answer 2

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.amazonaws.com',
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))

Answer 3

You don't need to construct a pre-signed URL to call an AWS AppSync endpoint. Set the authentication mode on the AppSync endpoint to AWS_IAM, grant permissions to your Lambda execution role, and then follow the steps in the "Building a JavaScript Client" tutorial to invoke a mutation or query.