// get user based on input from login form
var User = db.Users.Include(t => t.UserRole).Where(x => x.EmailAddress == emailAddress && x.Deleted == false).FirstOrDefault();

if (User != null) return false; // check user exists

// check user has permission to log in
if (!string.Equals(User.UserRole.RoleName, ValidRoleName, StringComparison.CurrentCultureIgnoreCase)) return false;
if (!Hashing.ValidatePassword(password, User.Password)) return false; // check input password matches user's password

// all checks pass, continue with the login here