Firebase login user with custom username

I'm developing an Android application in which the user is logging in using Firebase Email, Password authentication method. While registering users with Email and Password, I'm pushing other user profile data too in firebase realtime database like username, number address, etc. What I want to ask, Is this possible while logging in other than what Firebase asks to use email and password for login is this possible that I used the username instead of email and password should be the same which I entered while registering with email, password.

Here the tricky part is username is saved in DB but password is not as we know while registering with email and password nothing gets saved in DB. I will get a username by querying.

ref.child("credentials").orderByChild("usernames").equalTo(username).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                // **here how should I match that this username is of same user with email and password**

                }

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

But In the password field, I want to type the password that I entered with email while registering and that is not saved in DB so how should I get that and matched with each username accordingly that it is of the same username or not.