docs: @Override
    public TsiPeer extractPeer() throws GeneralSecurityException {
      Preconditions.checkState(!isInProgress(), "Handshake is not complete.");
      List<TsiPeer.Property<?>> peerProperties = new ArrayList<>();
      peerProperties.add(
          new TsiPeer.StringProperty(
              TSI_SERVICE_ACCOUNT_PEER_PROPERTY,
              handshaker.getResult().getPeerIdentity().getServiceAccount()));
      return new TsiPeer(peerProperties);
    }