A Go library to retrieve RSA public keys from a JWKS (JSON Web Key Set) endpoint.

Using Go modules

go get github.com/s12v/[email protected]

• github.com/square/go-jose - JWT library
• github.com/patrickmn/go-cache - default in-memory cache

GetEncryptionKey returns *jose.JSONWebKey for a given key id:

package main

import (
	"log"
	"time"

	"github.com/s12v/go-jwks"
	"github.com/square/go-jose"
)

func main() {
	jwksSource := jwks.NewWebSource("https://www.googleapis.com/oauth2/v3/certs")
	jwksClient := jwks.NewDefaultClient(
		jwksSource,
		time.Hour,    // Refresh keys every 1 hour
		12*time.Hour, // Expire keys after 12 hours
	)

	var jwk *jose.JSONWebKey
	jwk, err := jwksClient.GetEncryptionKey("c6af7caa0895fd01e778dceaa7a7988347d8f25c")
	if err != nil {
		log.Fatal(err)
	}

	log.Printf("key: %v, alg: %v, use: %v", jwk.KeyID, jwk.Algorithm, jwk.Use)
}

Log:

2018/07/30 01:22:35 Fetchng JWKS from https://www.googleapis.com/oauth2/v3/certs
2018/07/30 01:22:36 key: c6af7caa0895fd01e778dceaa7a7988347d8f25c, alg: RS256, use: sig

There are two caching parameters:

• refresh - the key will be fetched from the source after this interval
• ttl - if not used, the key will be deleted from cache

On the first request, the key is synchronously fetched from the key server and stored in the cache. On the next request after refresh interval, the key will be refreshed in the background (not affect response time). Only 1 key refresh is executed at the same time.

If the key is not requested during ttl interval, it will be removed from cache.

Default cache is github.com/patrickmn/go-cache in-memory cache. You can provide your own cache implementation, see cache.go:

type Cache interface {
	// Get an item from the cache and itsexpiration time.
	// Returns the item or nil, and a bool indicating whether the key was found
	GetWithExpiration(k string) (interface{}, time.Time, bool)
	// Add an item to the cache, replacing any existing item.
	Set(k string, x interface{})
}

and pass it to func NewClient(...)

Default source is WebSource. You can provide your own implementation, see source.go:

type JWKSSource interface {
	JSONWebKeySet() (*jose.JSONWebKeySet, error)
}