/**
 * When a user first uses Braze on a device they are considered "anonymous". Use this method to identify a user
 * with a unique ID, which enables the following:
 *
 * - If the same user is identified on another device, their user profile, usage history and event history will
 *   be shared across devices.
 * - If your app is used on the same browser by multiple people, you can assign each of them a unique identifier
 *   to track them separately. Only the most recent user on a particular browser will receive push
 *   notifications and in-app messages.
 *
 * When you request a user switch (which is any call to changeUser where the new user ID is not the same as the
 * existing user ID), the current session for the previous user (anonymous or not) is automatically ended and
 * a new session is started. Similarly, following a call to changeUser, any events which fire are guaranteed to
 * be for the new user -- if an in-flight server request completes for the old user after the user switch no
 * events will fire, so you do not need to worry about filtering out events from Braze for old users.
 *
 * Additionally, if you identify a user which has never been identified on another device, the entire history of
 * that user as an "anonymous" user on this device will be preserved and associated with the newly identified
 * user. However, if you identify a user which *has* been identified in another app, any history which was
 * already flushed to the server for the anonymous user on this device will be merged into the identified user.
 * Any fields that already exist on the identified user will not be overwritten, and the merge is limited
 * to the fields listed [here](https://www.braze.com/docs/api/endpoints/user_data/post_users_merge/).
 *
 * Note: Once you identify a user, you cannot revert to the "anonymous" user. The transition from anonymous to
 * identified tracking is only allowed once because the initial anonymous user receives special treatment to
 * allow for preservation of their history. As a result, we recommend against changing the user ID just because
 * your app has entered a "logged out" state because it makes you unable to target the previously logged out user
 * with re-engagement campaigns. If you anticipate multiple users on the same device, but only want to target one
 * of them when your app is in a logged out state, we recommend separately keeping track of the user ID you want
 * to target while logged out and switching back to that user ID as part of your app's logout process.
 *
 * @param userId - A unique identifier for this user. Limit 997 bytes.
 *   These User IDs should be private and not easily guessable (e.g. not a plain email address or username).
 *
 * @param signature - An encrypted signature to be used to authenticate the current user. You can update the signature
 *   using the [[`setSdkAuthenticationSignature`]] method. This signature will only have an effect if the `enableSdkAuthentication`
 *   initialization option is set to true.
 *
 * @returns - Returns a promise that the user change has been completed. You must wait for the promise to resolve before
 *   logging events or setting attributes or the events and attributes may not be associated with the correct user. The
 *   promise is rejected if the SDK is not initialized.
 */
export declare function changeUser(userId: string, signature?: string): Promise<void>;