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# Callback Authorization

## Overview

This section discusses the different authentication methods that can be used when passing in callback information in a request. If a callback is required, you must pass in certain elements in order to receive notifications on document generation and delivery.

## Callback container within a request

Users supply the Callback URL, and either a Username and Password or valid Token with the Generate, SelectAndGenerate, or SelectGenerateDeliver API to integrate with IEDocService in Expere Document Services. When determining whether to use a Username/Password or Token, you must specify either a value of `HTTPBasic` or `Token` within an `<AuthorizatioType/>` element.

AuthorizationHeaderOverride parameter: you may pass in a token value for this parameter within the `<Callback/>` container. When this value is passed, it will be used as the token header in the response. This allows headers to be ‘customizable’ and support callbacks to systems which can only receive tokens under certain header types.