[Docs]: Custom Authentication - Page Protection and Error Handling

[harshilp24]

Is there an existing issue for this?

• [X] I have searched the existing issues

Documentation Link

No response

Discord/slack/intercom Link

https://theappsmith.slack.com/archives/CNQ9Q91C0/p1711708876475579

Describe the problem and improvement.

This page needs a revamp. It doesn’t explain how to protect pages & how to handle error states- https://docs.appsmith.com/advanced-concepts/custom-authentication