How do I get the Firebase session id for my session?

if (user) {
  // User is signed in. var displayName = user.displayName; var email = user.email; var emailVerified = user.emailVerified; var photoURL = user.photoURL; var isAnonymous = user.isAnonymous; var uid = user.uid; var providerData = user.providerData;

  document.getElementById('quickstart-sign-in-status').textContent = 'Signed in';
  document.getElementById('quickstart-sign-in').textContent = 'Sign out';
  document.getElementById('quickstart-account-details').textContent = JSON.stringify(user, null, ' ');
  JSON.parse(user);
  sessionStorage.setItem('chave', user);
  var c = JSON.parse(sessionStorage.getItem('chave'));
  console.log(c);
}