adds the account info to the appropiate tables w/ the database.

Deletes the User account which cascades to delete their invoices too.

matches the client's username and pswd against the database if there's a match the user is logged in, otherwise there's an issue with username or password.

returns a user given the id if the id doesn't exist it error.

returns the list of all existing users.

http-status code for errors.

meant to be binded to new acct info.

meant to hold err strings related to authentication and account creation.