How to use Validate Data to trigger a custom error?

I have a login form and want to make the password field red, like a failed validation, when the password is incorrect. How can I do so?

I’m not using Wappler’s native passsword hashing functionality, so my Security Login step is actually after I check if the password is right or not:

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How can I use the “Validate Data” to trigger a custom error on a specific form field (password)?