Create Login Action in separate function call

[thoresuenert]

Discussion started in #474 , because we PRed from the wrong branch we had to open this PR.

The Example:
In the Samples/browser.php example the flow is shared between front and backend code and have the assumption that a tan is only required once during login.

If a tan is required the flow of actions is stopped and restarted where we left.

Our Goal here is a flow that fits all actions:
We want update a SEPA Account:

1. Login
2. GetBalance
3. GetNewTransaction
4. Logout/Close Connection

We assume that each step can require a tanRequest flow, so the process can stop on each step and have to restart with a tan (coupled or decoupled). We want to treat every situation the same:

1. POST Request /account/refresh to start the Process
2. Handle Exception: tan is needed, show user interaction for all tan requests a like
3. Continue with POST Request /account/refresh

Our Implementation

// $action is the action from the last call which needed a tan, or the action from the current step:
   $action = session()->pull('fints.action', $bank_connection->fints->createLoginAction());
// if the $action is from the last call and needs a tan and is not from this step:
// skip this step and continue with the next step
    if (! $action instanceof DialogInitialization) {
        return;
    }
// execute the action for the first time or try again with a tan
    $bank_connection->execute($action, $tan = request()->input('tan'));
// if the action needs a tan, fire an expcetion and show the tanRequest to the user
    if ($action->needsTan()) {
        $this->handleTanRequiredException($action);
    }

This is our idea of an implementation of the stop/restart mechanism the tanRequest needs.

[thoresuenert]

          Calling

        $this->requireTanMode();
        $this->ensureSynchronized();
        $this->messageNumber = 1;

inside of createLoginAction seems wrong to me.

I am not sure I understand the problem this PR is trying to solve.
If you continue after a TAN request, you don't need a login, otherwise you can always login, execute your actions and logout.

Originally posted by @ampaze in #474 (comment)

Should every execute of an action call $this->requireTanMode(); and $this->ensureSynchronized(); because in the mean time things can change?

[Philipp91]

I suggest you do this (not literally, but structurally):

function yourUserWantsToLogIn($credentials) {
  $action = $fints->login($credentials);
  commonTanHandling($action);
}

function yourUserWantsTheBalance() {
  $action = createBalanceAction();
  $fints->execute($action);
  commonTanHandling($action);
}

function commonTanHandling($action) {
  // The things you have above, without execute() calls and perhaps restructured a bit.
}

Note how the TAN handling needs to be implemented only in one place, no matter whether it's a login or a GetBalance or something else that requires the TAN.

[ampaze]

Should every execute of an action call $this->requireTanMode(); and $this->ensureSynchronized(); because in the mean time things can change?

No, I meant that these lines of code should be called when you want to login, not when you create the login action.