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main.go
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/
main.go
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package main
import (
"context"
"crypto/ecdsa"
"crypto/rsa"
"crypto/sha256"
"flag"
"fmt"
"log"
"math/big"
"net/http"
"os"
"time"
"github.com/pardot/oidc/discovery"
"gopkg.in/square/go-jose.v2"
"k8s.io/client-go/util/keyutil"
)
type config struct {
Issuer string
ListenAddr string
SAPublicPath string
}
func main() {
cfg := config{
ListenAddr: "0.0.0.0:8080",
SAPublicPath: "/etc/kubernetes/pki/sa.pub", // kubeadm default
}
flag.StringVar(&cfg.Issuer, "issuer", cfg.Issuer, "The OIDC issuer URL we are served at. Used as base URL for discovery (required)")
flag.StringVar(&cfg.SAPublicPath, "service-account-public-key-file", cfg.SAPublicPath, "Path to the SA signer _public_ key file (usually kube-apiserver --service-account-key-file flag value")
flag.StringVar(&cfg.ListenAddr, "listen", cfg.ListenAddr, "Address to listen for requests on")
flag.Parse()
if cfg.Issuer == "" || cfg.ListenAddr == "" || cfg.SAPublicPath == "" {
flag.Usage()
os.Exit(1)
}
mux := http.NewServeMux()
// do an initial key load to make sure it'll work, and work out the algs we
// deal with. We re-load it periodically, in case it's rolled out on us
if _, err := loadKeysFromFile(cfg.SAPublicPath); err != nil {
log.Fatalf("failed to load keyset: %v", err)
}
ks := &staticKeysource{path: cfg.SAPublicPath}
mux.Handle("/.well-known/openid-keys", discovery.NewKeysHandler(ks, 1*time.Minute))
md := discovery.ProviderMetadata{
Issuer: cfg.Issuer,
JWKSURI: cfg.Issuer + "/.well-known/openid-keys",
IDTokenSigningAlgValuesSupported: []string{string(jose.RS256), string(jose.ES256)},
// These aren't used, but are required to meet spec so serve up some
// data
AuthorizationEndpoint: cfg.Issuer + "/unused",
ResponseTypesSupported: []string{"id_token"},
SubjectTypesSupported: []string{"public"},
GrantTypesSupported: []string{"implicit"},
}
ch, err := discovery.NewConfigurationHandler(&md)
if err != nil {
log.Fatalf("creating configuration handler: %v", err)
}
mux.Handle("/.well-known/openid-configuration", ch)
mux.HandleFunc("/_health", func(w http.ResponseWriter, r *http.Request) {
if ks.lastErr != nil {
http.Error(w, "key read failure", http.StatusInternalServerError)
return
}
fmt.Fprint(w, "OK")
})
log.Printf("Serving at %s", cfg.ListenAddr)
if err := http.ListenAndServe(cfg.ListenAddr, mux); err != nil {
log.Fatalf("serving: %v", err)
}
}
var _ discovery.KeySource = (*staticKeysource)(nil)
type staticKeysource struct {
path string
lastErr error
}
func (s *staticKeysource) PublicKeys(ctx context.Context) (*jose.JSONWebKeySet, error) {
// the handler implentation does basic caching, so just re-read here
k, err := loadKeysFromFile(s.path)
if err != nil {
s.lastErr = err
return nil, err
}
// reset error, we're in OK state now
s.lastErr = nil
return &k, nil
}
func loadKeysFromFile(path string) (jose.JSONWebKeySet, error) {
raw, err := os.ReadFile(path)
if err != nil {
return jose.JSONWebKeySet{}, fmt.Errorf("reading %s: %v", path, err)
}
keys, err := keyutil.ParsePublicKeysPEM(raw)
if err != nil {
return jose.JSONWebKeySet{}, fmt.Errorf("parsing keys file %s: %w", path, err)
}
jwks := jose.JSONWebKeySet{}
for _, k := range keys {
var (
alg jose.SignatureAlgorithm
keyBytes []byte // internal format, to generate a stable ID
)
switch k := k.(type) {
case *rsa.PublicKey:
alg = jose.RS256
keyBytes = append(k.N.Bytes(), big.NewInt(int64(k.E)).Bytes()...)
case *ecdsa.PublicKey:
alg = jose.ES256
ecdhk, err := k.ECDH()
if err != nil {
return jose.JSONWebKeySet{}, fmt.Errorf("ec key to ecdh: %w", err)
}
keyBytes = ecdhk.Bytes()
default:
return jose.JSONWebKeySet{}, fmt.Errorf("invalid public key type: %T", k)
}
// generate a stable identifier we can refer to this key across runs with
h := sha256.New()
h.Write(keyBytes)
fp := fmt.Sprintf("%x", h.Sum(nil))[0:12]
jk := jose.JSONWebKey{
Key: k,
KeyID: fp,
Use: "sig",
Algorithm: string(alg),
}
if !jk.Valid() {
return jose.JSONWebKeySet{}, fmt.Errorf("internal error - invalid JWK generated")
}
jwks.Keys = append(jwks.Keys, jk)
}
return jwks, nil
}