re-authenticating a non-member causes an error

[NightJar]

Currently testing MTS, login type integration.

There is a Default Admin user, but that is all.

Discovery path:

1. attempt to gain access to the CMS: /admin
2. click Login under Login with RealMe® heading.
3. select Initiate SAML on the RealMe login service Messaging Test Site:SAML v2.0 AuthnRequest validation outcome interface
4. 👀 Observe the test site's homepage again.
5. attempt to gain access to the CMS: /admin
6. 👀 Observe the login form again
7. click Login under Login with RealMe® heading, again.
8. 👀 Observe login form presented, message Unfortunately we're not able to log you in through RealMe right now. Please try again shortly.
9. Use the member authenticator this time (Email & Password), default admin credentials
10. 👀 Observe a large PHP Emergency error: [Emergency] Uncaught BadMethodCallException: Object->__call(): the method 'getResponse' does not exist on 'SilverStripe\RealMe\Authenticator\LoginHandler' with an HTTP 500 response code.
11. Visit /admin - be logged in as normal.

You may have noticed between steps 7 and 8 above that the BackURL was altered from /admin/pages/ to /Secuirity/login/RealMe/acs. This triggers the manifestation, however this issue is really about the "not so nice" handling of an already authenticated session.

Alternate recreation steps:

1. Log in to CMS as default admin.
2. visit /Security/login
3. click the RealMe Login button.
4. 👀 Observe a large PHP Emergency error: [Emergency] Uncaught BadMethodCallException: Object->__call(): the method 'getResponse' does not exist on 'SilverStripe\RealMe\Authenticator\LoginHandler' with an HTTP 500 response code.

Trace
SilverStripe\View\ViewableData->__call(getResponse, Array) 
Security.php:393
SilverStripe\Security\Security::permissionFailure(SilverStripe\RealMe\Authenticator\LoginHandler, Array) 
LoginHandler.php:156
SilverStripe\RealMe\Authenticator\LoginHandler->acs(SilverStripe\Control\HTTPRequest) 
RequestHandler.php:323
SilverStripe\Control\RequestHandler->handleAction(SilverStripe\Control\HTTPRequest, acs) 
RequestHandler.php:202
SilverStripe\Control\RequestHandler->handleRequest(SilverStripe\Control\HTTPRequest) 
Security.php:911
SilverStripe\Security\Security->delegateToHandler(SilverStripe\RealMe\Authenticator\LoginHandler, Log in, Array) 
Security.php:880
SilverStripe\Security\Security->delegateToMultipleHandlers(Array, Log in, Array, Array) 
Security.php:710
SilverStripe\Security\Security->login(SilverStripe\Control\HTTPRequest) 
RequestHandler.php:323
SilverStripe\Control\RequestHandler->handleAction(SilverStripe\Control\HTTPRequest, login) 
Controller.php:284
SilverStripe\Control\Controller->handleAction(SilverStripe\Control\HTTPRequest, login) 
RequestHandler.php:202
SilverStripe\Control\RequestHandler->handleRequest(SilverStripe\Control\HTTPRequest) 
Controller.php:212
SilverStripe\Control\Controller->handleRequest(SilverStripe\Control\HTTPRequest) 
Director.php:360

The execution path comes through here

silverstripe-realme/src/Authenticator/LoginHandler.php

Line 100 in 3cdbc9d

$authData = $this->service->getAuthData();

down to here

silverstripe-realme/src/RealMeService.php

Lines 530 to 535 in 3cdbc9d

	if (!$auth->isAuthenticated()) {
	throw new RealMeException(
	'OneLogin SAML library did not successfully authenticate, but did not return a specific error',
	RealMeException::NOT_AUTHENTICATED
	);
	}

Log messages give
Error during RealMe authentication process. Code: 7, Message: OneLogin SAML library did not successfully authenticate, but did not return a specific error

Where Code 7 is PRIVATE_KEY_FILE_NOT_FOUND, where the code checks for code 8: SAML_RESPONSE_NOT_FOUND in what looks like an attempt to avoid this

silverstripe-realme/src/RealMeService.php

Lines 574 to 582 in 3cdbc9d

	} catch (OneLogin_Saml2_Error $e) {
	// If the Exception code indicates there wasn't a response, we ignore it as it simply means the visitor
	// isn't authenticated yet. Otherwise, we re-throw the Exception
	if ($e->getCode() === OneLogin_Saml2_Error::SAML_RESPONSE_NOT_FOUND) {
	return null;
	} else {
	throw $e;
	}
	}