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title: Limits for ext- Parameters in the Auth0 Login Redirect
slug: public-apis/limits-for-ext-parameters-in-the-auth0-login-redirect
createdAt: 2026-11-02T15:08:19.991Z
---

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**Topic type: Constraint**

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**Purpose**: Defines the Auth0 limits on `ext-` query parameters and the rule against sending payload data in them.

**Audience**: Engineers who modify the login redirect on pages they control.

**Applies to**: The Auth0 `/authorize` request used for login screening.

**Does not apply to**: Sign-up screening, which passes IDs in `user_metadata` instead.
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Before your page redirects the user to the Auth0 `/authorize` endpoint, it attaches the collector's IDs as custom query parameters that start with `ext-`. Auth0 enforces the following limits on these parameters. The two Accertify IDs, `deviceTransactionID` and `ubaID`, fit well within them.

## Auth0 Limits

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### Parameters per request

A maximum of 10 `ext-` parameters per `/authorize` request.
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### Parameter name

Up to 28 characters after `ext-`, matching `/^ext-[\w-]{1,28}$/`.
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### Parameter value

Up to 255 characters from a restricted set, matching `/^[-\w.*~@+ /:]{1,255}$/`.
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## Send ID References Only, Never Payload Data

Don't put device or behavioral payloads, such as `devicePayload` or `ubaEvents`, in `ext-` parameters. They are typically tens of kilobytes and won't fit the 255-character limit. Anything you attach here also passes through Auth0's infrastructure, so keep it to short, non-sensitive values.

Your collector already sends full payloads directly to Accertify. Accertify matches them to the login using the ID reference, so nothing else needs to travel through Auth0.



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**See also**:

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[Passing Device and Behavioral IDs to Auth0 at Login](docId:08m0hPxV6mwayd4ZUC1B0)
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[Auth0 Overview](docId:83YMYFB8wEXwmkEtJe9gH)
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