aws4fetch

What is aws4fetch?

The aws4fetch npm package is a utility for making HTTP requests to AWS services with AWS Signature Version 4 signing. It simplifies the process of signing requests to AWS services, allowing developers to interact with AWS APIs securely and efficiently.

What are aws4fetch's main functionalities?

Signing HTTP Requests

This feature allows you to sign HTTP requests to AWS services using AWS Signature Version 4. The code sample demonstrates how to create an instance of AwsClient with your AWS credentials and make a signed request to an AWS service endpoint.

const { AwsClient } = require('aws4fetch');

const aws = new AwsClient({
  accessKeyId: 'your-access-key-id',
  secretAccessKey: 'your-secret-access-key',
  sessionToken: 'your-session-token' // optional
});

const response = await aws.fetch('https://your-service.amazonaws.com/your-endpoint');
const data = await response.json();
console.log(data);

Customizing Request Options

This feature allows you to customize the HTTP request options such as method, headers, and body. The code sample shows how to make a POST request with custom headers and a JSON body to an AWS service endpoint.

const { AwsClient } = require('aws4fetch');

const aws = new AwsClient({
  accessKeyId: 'your-access-key-id',
  secretAccessKey: 'your-secret-access-key'
});

const response = await aws.fetch('https://your-service.amazonaws.com/your-endpoint', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({ key: 'value' })
});
const data = await response.json();
console.log(data);

Other packages similar to aws4fetch

aws-sdk

The aws-sdk package is the official AWS SDK for JavaScript, which provides a comprehensive set of tools for interacting with AWS services. It includes built-in support for request signing, similar to aws4fetch, but also offers a wide range of additional features such as service-specific clients, higher-level abstractions, and more extensive configuration options.

axios

While axios is a general-purpose HTTP client for Node.js and the browser, it can be used in conjunction with aws4 to sign requests to AWS services. Unlike aws4fetch, axios does not natively support AWS request signing, but it offers more flexibility and features for general HTTP request handling.

request

The request package is another popular HTTP client for Node.js that can be used with aws4 for signing AWS requests. Although request is now deprecated, it was widely used for making HTTP requests and could be extended with aws4 for AWS-specific use cases, similar to aws4fetch.

README

aws4fetch

A compact (6.4kb minified, 2.5kb gzipped) AWS client for environments that support fetch and SubtleCrypto – that is, modern web browsers and JS platforms like Cloudflare Workers. Also retries requests with an exponential backoff with full jitter strategy by default.

Example

import { AwsClient } from 'aws4fetch'

const aws = new AwsClient({ accessKeyId: MY_ACCESS_KEY, secretAccessKey: MY_SECRET_KEY })

// https://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html
const LAMBDA_FN_API = 'https://lambda.us-east-1.amazonaws.com/2015-03-31/functions'

async function invokeMyLambda(event) {
  const res = await aws.fetch(`${LAMBDA_FN_API}/my-lambda/invocations`, { body: JSON.stringify(event) })

  // `res` is a standard Response object: https://developer.mozilla.org/en-US/docs/Web/API/Response
  return res.json()
}

invokeMyLambda({my: 'event'}).then(json => console.log(json))

You can see a more detailed example, a Cloudflare Worker script you can use as a replacement for API Gateway, in the example directory.

API

aws4fetch exports two classes: AwsClient and AwsV4Signer

new AwsClient(options)

You can use the same instance of AwsClient for all your service calls as the service and region will be determined at fetch time – or you can create separate instances if you have different needs, eg no retrying for some service.

import { AwsClient } from 'aws4fetch'

const aws = new AwsClient({
  accessKeyId,     // required, akin to AWS_ACCESS_KEY_ID
  secretAccessKey, // required, akin to AWS_SECRET_ACCESS_KEY
  sessionToken,    // akin to AWS_SESSION_TOKEN if using temp credentials
  service,         // AWS service, by default parsed at fetch time
  region,          // AWS region, by default parsed at fetch time
  cache,           // credential cache, defaults to `new Map()`
  retries,         // number of retries before giving up, defaults to 10, set to 0 for no retrying
  initRetryMs,     // defaults to 50 – timeout doubles each retry
})

Promise<Response> aws.fetch(input[, init])

Has the same signature as the global fetch function

import { AwsClient } from 'aws4fetch'

const aws = new AwsClient(opts)

async function doFetch() {

  const response = await aws.fetch(url, {

    method,  // if not supplied, will default to 'POST' if there's a body, otherwise 'GET'
    headers, // standard JS object literal, or Headers instance
    body,    // optional, String or ArrayBuffer/ArrayBufferView – ie, remember to stringify your JSON

    // and any other standard fetch options, eg keepalive, etc

    // optional, largely if you want to override options in the AwsClient instance
    aws: {
      signQuery,          // set to true to sign the query string instead of the Authorization header
      accessKeyId,        // same as in AwsClient constructor above
      secretAccessKey,    // same as in AwsClient constructor above
      sessionToken,       // same as in AwsClient constructor above
      service,            // same as in AwsClient constructor above
      region,             // same as in AwsClient constructor above
      cache,              // same as in AwsClient constructor above
      datetime,           // defaults to now, to override use the form '20150830T123600Z'
      appendSessionToken, // set to true to add X-Amz-Security-Token after signing, defaults to true for iot
      allHeaders,         // set to true to force all headers to be signed instead of the defaults
      singleEncode,       // set to true to only encode %2F once (usually only needed for testing)
    },
  })

  console.log(await response.json())
}

NB: Due to the way bodies are handled in Request instances, it's faster to invoke the function as above – using a URL as the input argument and passing the body in the init argument – instead of the form of invocation that uses a Request object directly as input.

If you don't know which URL to call for the AWS service you want, the full list of AWS endpoints can be found here: https://docs.aws.amazon.com/general/latest/gr/rande.html

And the APIs are documented here: https://docs.aws.amazon.com/ (the REST APIs are usually documented under "API Reference" for each service)

Promise<Request> aws.sign(input[, init])

Returns a Promise that resolves to an AWS4 signed Request – has the same signature as fetch. Use this to create a Request you can send using fetch() yourself.

import { AwsClient } from 'aws4fetch'

const aws = new AwsClient(opts)

async function doFetch() {

  const request = await aws.sign(url, {

    method,  // if not supplied, will default to 'POST' if there's a body, otherwise 'GET'
    headers, // standard JS object literal, or Headers instance
    body,    // optional, String or ArrayBuffer/ArrayBufferView – ie, remember to stringify your JSON

    // and any other standard fetch options, eg keepalive, etc

    // optional, largely if you want to override options in the AwsClient instance
    aws: {
      signQuery,          // set to true to sign the query string instead of the Authorization header
      accessKeyId,        // same as in AwsClient constructor above
      secretAccessKey,    // same as in AwsClient constructor above
      sessionToken,       // same as in AwsClient constructor above
      service,            // same as in AwsClient constructor above
      region,             // same as in AwsClient constructor above
      cache,              // same as in AwsClient constructor above
      datetime,           // defaults to now, to override use the form '20150830T123600Z'
      appendSessionToken, // set to true to add X-Amz-Security-Token after signing, defaults to true for iot
      allHeaders,         // set to true to force all headers to be signed instead of the defaults
      singleEncode,       // set to true to only encode %2F once (usually only needed for testing)
    },
  })

  const response = await fetch(request)

  console.log(await response.json())
}

new AwsV4Signer(options)

The underlying signing class for a request – use this if you just want to deal with the raw AWS4 signed method/url/headers/body.

import { AwsV4Signer } from 'aws4fetch'

const signer = new AwsV4Signer({
  url,                // required, the AWS endpoint to sign
  accessKeyId,        // required, akin to AWS_ACCESS_KEY_ID
  secretAccessKey,    // required, akin to AWS_SECRET_ACCESS_KEY
  sessionToken,       // akin to AWS_SESSION_TOKEN if using temp credentials
  method,             // if not supplied, will default to 'POST' if there's a body, otherwise 'GET'
  headers,            // standard JS object literal, or Headers instance
  body,               // optional, String or ArrayBuffer/ArrayBufferView – ie, remember to stringify your JSON
  signQuery,          // set to true to sign the query string instead of the Authorization header
  service,            // AWS service, by default parsed at fetch time
  region,             // AWS region, by default parsed at fetch time
  cache,              // credential cache, defaults to `new Map()`
  datetime,           // defaults to now, to override use the form '20150830T123600Z'
  appendSessionToken, // set to true to add X-Amz-Security-Token after signing, defaults to true for iot
  allHeaders,         // set to true to force all headers to be signed instead of the defaults
  singleEncode,       // set to true to only encode %2F once (usually only needed for testing)
})

Promise<{ method, url, headers, body }> signer.sign()

Actually perform the signing of the request and return a Promise that resolves to an object containing the signed method, url, headers and body.

method will be a String, url will be an instance of URL, headers will be an instance of Headers and body will unchanged from the argument you supply to the constructor.

import { AwsV4Signer } from 'aws4fetch'

const signer = new AwsV4Signer(opts)

async function sign() {
  const { method, url, headers, body } = await signer.sign()

  console.log(method, url, [...headers], body)
}

Promise<String> signer.authHeader()

Returns a Promise that resolves to the signed string to use in the Authorization header

Used by the sign() method – you shouldn't need to access this directly unless you're constructing your own requests.

Promise<String> signer.signature()

Returns a Promise that resolves to the hex signature

Used by the sign() method – you shouldn't need to access this directly unless you're constructing your own requests.

Installation

With npm do:

npm install aws4fetch