IdentityProvider

// Iframe displaying a page from the https://idp.example origin
const userInfo = await IdentityProvider.getUserInfo({
  configURL: "https://idp.example/fedcm.json",
  clientId: "client1234",
});

// IdentityProvider.getUserInfo() returns an array of user information.
if (userInfo.length > 0) {
  // Returning accounts should be first, so the first account received
  // is guaranteed to be a returning account
  const name = userInfo[0].name;
  const givenName = userInfo[0].given_name;
  const displayName = givenName || name;
  const picture = userInfo[0].picture;
  const email = userInfo[0].email;

  // …

  // Render a personalized sign-in button using the information returned above
}