fastify-hmac

Fastify plugin for HMAC signature validation.

How it works

Verifies that http messages are signed according to IETF draft standards.

Install

npm i @autotelic/fastify-hmac

Usage

Registering the plugin will decorate the fastify request instance with a validateHMAC method, and add a pre-validation hook to verify the HMAC signature of requests.

const hmac = require('@autotelic/fastify-hmac')

async function app (fastify, options) {
  fastify.register(hmac, {
    sharedSecret: 'topSecret',
    algorithmMap: {
      hs2019: {
        'my-key-a': 'sha512',
        'my-key-b': 'sha256'
      }
    }
  })

  const hmacLogger = (error) => {
    if (error) {
      fastify.log.info(error.message)
    } else {
      fastify.log.info('HMAC Validated.')
    }
  }

  fastify.get('/foo', async (request, reply) => {
    request.validateHMAC(hmacLogger)
    reply.send({ foo: 'bar' })
  })
}

module.exports = app

API

PluginOpts : Object

Properties

Name	Type	Description
sharedSecret	string	Secret used by client to generate signatures. (required)
algorithmMap	{ [algorithm]: { [keyId]: string } }	Maps the Signature header algorithm and keyId properties to a specific algorithm. (required, unless providing getAlgorithm)
verificationError	(string) => Error	Receives the original error message and returns a new error. By default, all errors returned are generic Unauthenticated http errors. This is to prevent sending sensitive error data to the client. (optional)
digestEncoding	string	Defaults to 'base64'. (optional)
getDigest	(FastifyRequest, PluginOpts) => string	Calculates and verifies a message Digest header to be used as input to the HMAC signature. (optional)
extractSignature	(FastifyRequest, PluginOpts) => string	Extracts properties from the Signature Header constructed according to IETF draft standards. (optional)
constructSignatureString	(FastifyRequest, PluginOpts) => string	Constructs a signature digest string from the key material detailed in the Signature header according to IETF draft standards. (optional)
getAlgorithm	(FastifyRequest, PluginOpts) => string	Returns an HMAC algorithm. By default this will use the keyId and algorithm values from the Signature header, to pull the appropriate value from the algorithmMap. (optional)
getSignatureEncoding	(FastifyRequest, PluginOpts) => string	Returns the encoding to be used during HMAC signature construction. (optional - defaults to () => 'base64')
validateRequests	boolean	If true will add a preValidation hook to validate HMAC signatures. (optional - defaults to true)

validateHMAC: Function

Arguments

Name	Type	Description
callback	(Error?) => any	Called with no args when HMAC validation is successful, and called with the error on failure. (optional)

Return

If no callback is provided the validateHMAC request decorator will return true if HMAC validation is successful, and will return an Error if HMAC validation fails (the Error wil be returned, not thrown).

Examples:

Basic

npm run example:basic

Shopify

npm run example:shopify

License

MIT