Fix OpenBao OIDC token exchange compatibility

src/internal/server/oidc/session.go

@@ -15,6 +15,7 @@ type PKCESession struct {
 	PKCEChallenge       string    // S256 challenge
 	PKCEChallengeMethod string    // always "S256"
 	State               string
+	Nonce               string
 	Username            string    // set after auth
 	Scopes              []string
 	ExpiresAt           time.Time