fix pkce implementation

Initial implementation was using the same verifier during
the lifetime of the agent instance.
Now instanciated a pkce verifier at each authorization.

go.mod

@@ -5,6 +5,7 @@ go 1.22
 require (
 	github.com/coreos/go-oidc/v3 v3.11.0
 	github.com/go-ldap/ldap/v3 v3.4.8
+	github.com/go-pkgz/expirable-cache/v3 v3.0.0
 	github.com/negasus/haproxy-spoe-go v1.0.5
 	github.com/sirupsen/logrus v1.9.3
 	github.com/spf13/viper v1.19.0

go.sum

@@ -32,6 +32,8 @@ github.com/go-jose/go-jose/v4 v4.0.2 h1:R3l3kkBds16bO7ZFAEEcofK0MkrAJt3jlJznWZG0
 github.com/go-jose/go-jose/v4 v4.0.2/go.mod h1:WVf9LFMHh/QVrmqrOfqun0C45tMe3RoiKJMPvgWwLfY=
 github.com/go-ldap/ldap/v3 v3.4.8 h1:loKJyspcRezt2Q3ZRMq2p/0v8iOurlmeXDPw6fikSvQ=
 github.com/go-ldap/ldap/v3 v3.4.8/go.mod h1:qS3Sjlu76eHfHGpUdWkAXQTw4beih+cHsco2jXlIXrk=
+github.com/go-pkgz/expirable-cache/v3 v3.0.0 h1:u3/gcu3sabLYiTCevoRKv+WzjIn5oo7P8XtiXBeRDLw=
+github.com/go-pkgz/expirable-cache/v3 v3.0.0/go.mod h1:2OQiDyEGQalYecLWmXprm3maPXeVb5/6/X7yRPYTzec=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
@@ -61,6 +63,9 @@ github.com/hashicorp/go-uuid v1.0.3 h1:2gKiV6YVmrJ1i2CKKa9obLvRieoRGviZFL26PcT/C
 github.com/hashicorp/go-uuid v1.0.3/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/bN7x4byOro=
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
+github.com/hashicorp/golang-lru v0.5.4 h1:YDjusn29QI/Das2iO9M0BHnIbxPeyuCHsjMW+lJfyTc=
+github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=
+github.com/hashicorp/golang-lru/v2 v2.0.7/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyfM2/ZepoAG6RGpeM=
 github.com/hashicorp/hcl v1.0.0 h1:0Anlzjpi4vEasTeNFn2mLJgTSwt0+6sfsiTG8qcWGx4=
 github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=
 github.com/jcmturner/aescts/v2 v2.0.0 h1:9YKLH6ey7H4eDBXW8khjYslgyqG2xZikXP0EQFKrle8=

internal/auth/authenticator_oidc.go

@@ -15,6 +15,7 @@ import (
 	"github.com/vmihailenco/msgpack/v5"
 
 	"github.com/coreos/go-oidc/v3/oidc"
+	cache "github.com/go-pkgz/expirable-cache/v3"
 	action "github.com/negasus/haproxy-spoe-go/action"
 	message "github.com/negasus/haproxy-spoe-go/message"
 
@@ -74,7 +75,7 @@ type OIDCAuthenticator struct {
 
 	signatureComputer *HmacSha256Computer
 	encryptor         *AESEncryptor
-	pkceVerifier      string
+	pkceVerifierCache cache.Cache[string, string]
 
 	options OIDCAuthenticatorOptions
 }
@@ -120,7 +121,7 @@ func NewOIDCAuthenticator(options OIDCAuthenticatorOptions) *OIDCAuthenticator {
 		options:           options,
 		signatureComputer: NewHmacSha256Computer(options.SignatureSecret),
 		encryptor:         NewAESEncryptor(options.EncryptionSecret),
-		pkceVerifier:      oauth2.GenerateVerifier(),
+		pkceVerifierCache: cache.NewCache[string, string](),
 	}
 
 	go func() {
@@ -396,8 +397,15 @@ func (oa *OIDCAuthenticator) buildAuthorizationURL(domain string, oauthArgs OAut
 	}
 
 	var authorizationURL string
+	pkceVerifier := oauth2.GenerateVerifier()
+	stateStr := base64.StdEncoding.EncodeToString(stateBytes)
+	cacheTTL := time.Second * 3600
+	if oa.options.CookieTTL != 0 {
+		cacheTTL = oa.options.CookieTTL
+	}
+	oa.pkceVerifierCache.Set(stateStr, pkceVerifier, cacheTTL)
 	err = oa.withOAuth2Config(domain, func(config oauth2.Config) error {
-		authorizationURL = config.AuthCodeURL(base64.StdEncoding.EncodeToString(stateBytes), oauth2.S256ChallengeOption(oa.pkceVerifier))
+		authorizationURL = config.AuthCodeURL(stateStr, oauth2.S256ChallengeOption(pkceVerifier))
 		return nil
 	})
 	if err != nil {
@@ -435,9 +443,15 @@ func (oa *OIDCAuthenticator) handleOAuth2Callback(tmpl *template.Template, error
 
 		domain := extractDomainFromHost(r.Host)
 
+		pkceVerifier, ok := oa.pkceVerifierCache.Get(stateB64Payload)
+		if !ok {
+			logrus.Error("cannot retrieve pkce verifier")
+			http.Error(w, "Bad request", http.StatusBadRequest)
+			return
+		}
 		var oauth2Token *oauth2.Token
 		err := oa.withOAuth2Config(domain, func(config oauth2.Config) error {
-			token, err := config.Exchange(r.Context(), r.URL.Query().Get("code"), oauth2.VerifierOption(oa.pkceVerifier))
+			token, err := config.Exchange(r.Context(), r.URL.Query().Get("code"), oauth2.VerifierOption(pkceVerifier))
 			oauth2Token = token
 			return err
 		})