/**
 * Adds an an alias for the user.  (alias, label) pairs can exist on one and only one user.
 * If a different user already has this alias or external user id, the alias attempt will be rejected
 * on the server.
 *
 * @param alias - An identifier for this user.
 * @param label - A label for the alias.  e.g. the source of the alias, like "internal_id"
 *
 * @returns Resolves to a boolean that indicates whether the update was successfully enqueued. Resolves to undefined
 *   if the SDK is not initialized.
 */
export declare function addUserAlias(alias: string, label: string): Promise<boolean | undefined>;