How to store data from forms then use it as flow condition

hello!
i’m creating my very first app ever, and i’m using flowable and postgree.

my app is basically a student platform that allows people to log in then to see their class schedules.
the accounts are created via a form (flowable form) & the log in is also a form.
i created a choice gate after the start that would send a user to “create an account” if his mail is not already registered

i noticed that all the data i enter via the forms gets stored automatically in a table called “act_hi_varinst”
i want to find a way to store this data, then with the flow condition, compare if the entered mail exists already or not

how would that be possible ? thank you in advance!

here’s my process model (for now i’m ignoing the check wether the password is correct or not)

Hi!
If the login form in the first task has a field with id “password”, a process instance variable is available to you. Into the exclusive gateway you can use it into a flow condition, such as #{password != null}

For checking if the password is correct respect to your database, you should add a service task making a call to your service for checking username and password.

Hope it helps