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authenticator.go
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authenticator.go
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package jwt
import (
"crypto/rsa"
"encoding/json"
"fmt"
"net/http"
"strings"
"time"
_jwt "github.com/cristalhq/jwt/v3"
"go.uber.org/zap"
"gopkg.in/square/go-jose.v2"
)
type JWTAuthenticator struct {
jose.JSONWebKeySet
verifier map[string]_jwt.Verifier
logger *zap.Logger
}
func NewJWTAuthenticator(gitlab string) (*JWTAuthenticator, error) {
logger, err := zap.NewProduction()
l := logger.With(zap.String("gitlab", gitlab))
if err != nil {
return nil, err
}
r, err := http.Get(fmt.Sprintf("%s/-/jwks", gitlab))
if err != nil {
l.Error("can't fetch Gitlab's jwks", zap.Error(err))
return nil, err
}
if r.StatusCode != http.StatusOK {
l.Error("can't fetch Gitlab's jwks", zap.Int("status", r.StatusCode))
return nil, fmt.Errorf("GET jwks bad status: %d", r.StatusCode)
}
defer r.Body.Close()
var j JWTAuthenticator
err = json.NewDecoder(r.Body).Decode(&j)
if err != nil {
l.Error("can't parse Gitlab's jwks JSON", zap.Error(err))
return nil, err
}
j.logger = logger
j.verifier = make(map[string]_jwt.Verifier)
for _, k := range j.Keys {
if k.Use != "sig" {
continue
}
alg := _jwt.Algorithm(k.Algorithm)
l = l.With(zap.String("kid", k.KeyID), zap.String("algo", k.Algorithm))
var err error
switch {
case strings.HasPrefix(k.Algorithm, "HS"):
j.verifier[k.KeyID], err = _jwt.NewVerifierHS(alg, k.Key.([]byte))
case strings.HasPrefix(k.Algorithm, "RS"):
j.verifier[k.KeyID], err = _jwt.NewVerifierRS(alg, k.Key.(*rsa.PublicKey))
default:
err = fmt.Errorf("unhandled algo : %s %v", k.Algorithm, k)
}
if err != nil {
l.Error("Bad signer", zap.Error(err))
return nil, err
}
l.Info("a signer")
}
return &j, err
}
func (j *JWTAuthenticator) VerifySignature(t *_jwt.Token) error {
l := j.logger.With(zap.ByteString("jwt", t.Raw()))
for _, k := range j.Key(t.Header().KeyID) {
if k.Algorithm != t.Header().Algorithm.String() {
err := fmt.Errorf("algo mismatch : %s vs %s", k.Algorithm, t.Header().Algorithm.String())
l.Error("Bad algo", zap.Error(err))
return err
}
err := j.verifier[k.KeyID].Verify(t.Payload(), t.Signature())
if err != nil {
l.Error("verification faild", zap.Error(err))
return err
}
var claims _jwt.StandardClaims
err = json.Unmarshal(t.RawClaims(), &claims)
if err != nil {
l.Error("can't parse standard claims JSON", zap.Error(err))
return err
}
if claims.ExpiresAt != nil && time.Now().After(claims.ExpiresAt.Local()) {
err = fmt.Errorf("expired token %v", claims.ExpiresAt.Time)
l.Error("Expired", zap.Error(err))
return err
}
if claims.NotBefore != nil && claims.NotBefore.Local().After(time.Now()) {
err = fmt.Errorf("not before token %v", claims.NotBefore.Time)
l.Error("Not before", zap.Error(err))
return err
}
return nil
}
err := fmt.Errorf("can't authenticate key %v", t)
l.Warn("Signer not found")
return err
}
func (j *JWTAuthenticator) ParseAndVerifySignature(jwtRaw string) (*_jwt.Token, error) {
token, err := _jwt.ParseString(jwtRaw)
if err != nil {
j.logger.Warn("Can't parse JWT", zap.Error(err))
return nil, err
}
err = j.VerifySignature(token)
if err != nil {
return nil, err
}
return token, nil
}