Is best practice to Web Application users credentials using same database users credentials
It is certainly possible to use database usernames to authenticate web application users, but that is rather uncommon.
End users are typically authenticated at the enterprise level - meaning they use the same identity in a single-sign-on fashion to identify themselves with multiple enterprise applications.
Then in web applications, those identities are mapped to a small number of specific database users with capabilities matching the roles/profiles of the end users.
Having all enterprise users (and much less end users) defined in all databases becomes a logistic nightmare once the number exceeds a few ten's of users. It is definitely not possible once you start having end-users/customers accounts going rapidly into the millions.