async function registerUser(username: string, password: string) {
  try {
    const { client_id, client_secret } = await authAPI.registerUser(username, password);

    // get tokens
    const {
      access_token,
      refresh_token,
      refreshTokenExpiresAt,
    } = await authAPI.getUserAccessToken(username, password, client_id, client_secret);

    // save to async storage
    store.update('user', {
      client_id,
      client_secret,
      access_token,
      refresh_token,
      refreshTokenExpiresAt,
    });
  } catch (err) {
    throw Error(err);
  }
}