certificate := r.TLS.PeerCertificates[0]
	if !globalIAMSys.STSTLSConfig.InsecureSkipVerify { // Verify whether the client certificate has been issued by a trusted CA.
		_, err := certificate.Verify(x509.VerifyOptions{
			KeyUsages: []x509.ExtKeyUsage{
				x509.ExtKeyUsageClientAuth,
			},
			Roots: globalRootCAs,
		})
		if err != nil {
			writeSTSErrorResponse(ctx, w, ErrSTSInvalidClientCertificate, err)
			return
		}