Can Drupal 8 security tables be modified?

I need to add another layer or field to the log-in of Drupal, is that possible? Basically, I’d like to modify the Drupal security table to have that 1 field as part of the log-in credentials. I’ve searched the documentations and haven’t found any resources that points me to my questions. I basically need to create a front-end app using Angular JS and will have an extra field for the log-in so not sure how to accomplish this.

I’d appreciate if you can point me to the right direction and what I need to do to get me started. I sincerely appreciate any help you can provide.

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