Move the "authorize only" & "authorize and capture" transaction mode settings into the payment gateways

I agree. We should add the setting to payment gateways. A lot of times I forget, even, we customize it on checkout.

This issue helps us realign with the most common use case. Someone has one payment gateway (maybe two) and one checkout flow.

The special use case should be overriding the transaction type per-checkout flow. Such as a digital checkout. Most users probably have a mixed checkout flow that would use the default.

So we need to add a capture setting to the payment gateway configuration schema

  mapping:
    capture:
      type: boolean
      label: 'Default transaction mode'

The form can say some diddy about how payments create with this gateway will use that mode. But it can be overridden per-checkout flow instance.

In the PaymentProcess pane we need another option for capture. Basically "Use default transaction mode". Some kind of checkbox which hides the radios.

  /**
   * {@inheritdoc}
   */
  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
    $form = parent::buildConfigurationForm($form, $form_state);
    $form['capture'] = [
      '#type' => 'radios',
      '#title' => $this->t('Transaction mode'),
      '#description' => $this->t('This setting is only respected if the chosen payment gateway supports authorizations.'),
      '#options' => [
        TRUE => $this->t('Authorize and capture'),
        FALSE => $this->t('Authorize only (requires manual capture after checkout)'),
      ],
      '#default_value' => (int) $this->configuration['capture'],
    ];

    return $form;
  }

Then anywhere we check for the capture value we'll need to check if default and pull from the payment gateway

     try {
        $payment->payment_method = $this->order->get('payment_method')->entity;
        $payment_gateway_plugin->createPayment($payment, $this->configuration['capture']);
        $this->checkoutFlow->redirectToStep($next_step_id);
      }

We could initialize a $capture variable below these lines

    $payment = $this->createPayment($payment_gateway);
    $next_step_id = $this->checkoutFlow->getNextStepId($this->getStepId());

Something like

$capture = $this->configuration['capture'] ?? $payment_gateway_plugin->getTransactionMode()

It would be helpful if there was also a way to control the transaction mode apart from the gateways. A third-party fraud detection service could be used during checkout to pre-authorize the payment transaction. If the responses returned by the detection service include "pending" or "under review" in addition to strict approve/deny results, we'd want to set the transaction mode to "authorize only" instead of the default "authorize and capture" for pre-approved transactions.

Perhaps instead of:

$capture = $this->configuration['capture'] ?? $payment_gateway_plugin->getTransactionMode()

Create a new method for the checkout pane with default implementation that could be overridden by extending the class:

protected function getTransactionCapture(PaymentGatewayInterface $payment_gateway_plugin) {
  if ($payment_gateway_plugin instanceof SupportsConditionalPaymentCapture) {
    return $payment_gateway_plugin->getTransactionMode($this->order);
  }
  else {
    return $this->configuration['capture'];
  }
}

And then this:

$capture = $this->configuration['capture'] ?? $this->getTransactionCapture($payment_gateway_plugin);

Dumping some thoughts. I saw this Slack convo and it rolled in my brain yesterday afternoon

When we first added the auth or auth+capture setting, in hindsight I wish we kept it on the payment gateway and then one of the following:

1. You used conditions to control which payment gateway (auth or auth+capture) was used on checkout flows
2. The checkout flow pane was an override behavior

For backwards compatibility, #2 is the best. Whereas #1 provides better visibility (possibly, we don't show conditions on the gateway collection list.)

So the gateway should dictate default behavior. Then the checkout flow can have:

- Use default behavior
- Only authorize, overriding defaults
- Always capture, overriding defaults