How to use the @esri/arcgis-rest-auth.UserSession function in @esri/arcgis-rest-auth

.then(sessionInfo => {
        console.log(sessionInfo);
        const newSession = new UserSession(session);

        // if we are in a browser (client side) we are working with an instance
        // of `UserSession` otherwise (server side) we are working with a JSON
        // representation of a session.
        if (process.browser) {
          this.store.set({ session: newSession });

          // if we are in a browser we should also update IdentityManager
          loadModules(["esri/identity/IdentityManager"]).then(([esriId]) => {
            esriId.registerToken(session.toCredential());
          });
        } else {
          this.store.set({ session: sessionInfo });
        }

        return error.retry(newSession, 1);

preload({ params }) {
      const { session } = this.store.get();

      // redirect to the homepage unless the user is signed in
      if (!session) {
        this.redirect(302, "/");
        return;
      }

      const { webmapId } = params;

      // if we are on the server we won't have an actuall UserSession just a
      // JSON representation of one. So we need to hydrate a UserSession.
      const userSession = process.browser ? session : new UserSession(session);

      // next we can request both the webmap item and the webmap data (the JSON)
      // and process the data to get a list of layers.
      return Promise.all([
        getItem(webmapId, {
          authentication: userSession
        }).catch(error => {
          return retryWithNewSession(error, this.fetch);
        }),
        getItemData(webmapId, {
          authentication: userSession
        }).catch(error => {
          return retryWithNewSession(error, this.fetch);
        })
      ]).then(([item, webmap]) => {
        const layers = webmap.operationalLayers

store: data => {
    // `data` is whatever was in the Store on the server side.
    // if we have a session we can create a new UserSession that we can
    // use with ArcGIS REST JS on the client.
    return new Store({
      session: data && data.session ? new UserSession(data.session) : null,
      user: data.user,
      org: data.org
    });
  }
});

.then(({ username, password }) => {
      session = new UserSession({
        username,
        password
      });

      // this will generate a token and use it to get into about a user
      return session.getUser();
    })
    .then(self => {

preload() {
      const { session } = this.store.get();

      // redirect to the homepage unless the user is signed in
      if (!session) {
        this.redirect(302, "/");
        return;
      }

      // if we are on the server we won't have an actuall UserSession just a
      // JSON representation of one. So we need to hydrate a UserSession.
      const userSession = process.browser ? session : new UserSession(session);

      // now we can search for webmaps. Sapper will wait until this promise
      // resolves before rendering the page.
      return (
        searchItems({
          q: `owner:${session.username} type:"Web Map"`,
          num: 100,
          authentication: userSession
        })
          // if there is an error we can retry the request with a fresh session
          // from /auth/exchange-token
          .catch(error => {
            return retryWithNewSession(error, this.fetch);
          })
          // then we can process out response.
          .then(response => {

export function createRuntimeMockUserSession (
  now: number
): UserSession {
  const tomorrow = new Date(now + 86400000);
  return new UserSession({
    clientId: "clientId",
    redirectUri: "https://example-app.com/redirect-uri",
    token: "fake-token",
    tokenExpires: tomorrow,
    refreshToken: "refreshToken",
    refreshTokenExpires: tomorrow,
    refreshTokenTTL: 1440,
    username: "casey",
    password: "123456",
    portal: "https://myorg.maps.arcgis.com/sharing/rest"
  });
}