[Vuejs]-How to prevent user authentication in Firebase/Vue.js BEFORE email is verified

This has been discussed quite a few times already: there is currently no way to prevent a user from signing in with an unverified email address. But you can check the verification status both in your client-side code, and in your back-end code (or security rules) to ensure that only users with a verified email address have access to your resources.

See:

• How do I lock down Firebase Database to any user from a specific (email) domain?
• Firebase Prevent Creating Account Before Email Verification
• more similar questions