Better handling of cancellations/errors

[kinglozzer]

E.g. with Facebook login, clicking “Cancel” redirects the user to:

mysite.com/oauth/callback?error=access_denied&error_code=200&error_description=Permissions%20error&error_reason=user_denied&state=...

[madmatt]

At the moment this just results in an HTTP 400 response, which is the same response as if the OAuth response was not returned at all (even though one is a failure case and the other is a recoverable error).

I'll probably try and work on this sometime soon as we'll need it for a project we're working on, @kinglozzer do you have any thoughts on how you'd ideally want this solved?

FWIW: I'm working on this as part of an upgrade from SS3, where the previous project used the now-deprecated BetterBrief/silverstripe-opauth module. That handled it by having two methods - getSuccessBackURL() and getCantLoginBackURL() which are called if the OAuth response was successful or not. I've built those into a custom TokenHandler for now, but this logic is part of the Controller class rather than the TokenHandler, so is a few steps too early in the controller context...

[kinglozzer]

As is tradition, I opened this issue, forgot about it for a while, and now can’t remember how half of this works...

When I looked at it before, there was no real consistency between providers and how they provide error messages/codes, so I think ideally it should be possible to add relevant error handling for each provider & context. Perhaps we could use a similar approach the TokenHandler classes? Pseudo-code:

Bigfork\SilverStripeOAuth\Client\Control\Controller:
  error_handlers:
    genericerrorhandler:
      priority: 1
      context: '*'
      class: 'OAuthGenericErrorHandler'

catch (Exception $e) {
    $message = $e->getMessage();
    $handlers = $this->getErrorHandlersForContext($session->get('oauth2.context'));
    // Run handlers to process the error message
    $results = [];
    foreach ($handlers as $handlerConfig) {
        $handler = Injector::inst()->create($handlerConfig['class']);
        $results[] = $handler->handleError($message, $provider, $request);
    }

    foreach ($results as $result) {
        if ($result instanceof HTTPResponse) {
            return $result;
        }
    }

    // Redirect to login form and show $message
}

use Bigfork\SilverStripeOAuth\Client\Handler\ErrorHandler;

class OAuthGenericErrorHandler implements ErrorHandler
{
    public function handleError(&$message, $provider, $request)
    {
        if ($provider instanceof FacebookProvider) {
            switch ($request->getVar('error_code') {
                case '200':
                    $message = 'You clicked no, plz click yes.';
                    break;
                // ...
            }
        }
    }
}

What do you think?

[kinglozzer]

Resolved by #13 and https://github.com/bigfork/silverstripe-oauth-login/commit/7c0b6c49cf0f046a414a264153ff86217239f9a0