docs: Fix sample code to avoid reading from undefined in didAuthError

[ghengeveld]

Summary

This updates an example code snippet to prevent reading status from undefined.
According to the type definitions, response may be undefined. I can confirm because this happened in production.

Set of changes

• Updated docs/advanced/authentication.md to add an optional chaining operator to handle undefined response.

[changeset-bot]

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Latest commit: dfd53e6

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