Improve error message when required attributes are missing

This issue is imported from pivotal - Originaly created at Apr 9, 2020 by Peter Havekes

The log shows:

messages:Apr  8 13:57:53 sa-test-app.surfconext.nl stepup-selfservice[119612]: {"channel":"app","level":"ERROR","message":"Uncaught PHP Exception Symfony\\Component\\HttpKernel\\Exception\\HttpException: \"Missing value for required attribute \"commonName\"\" at /opt/stepup/Stepup-SelfService-3.1.0-20200123094957Z-899924d0139418958a9e502aa52eeea34494053d/vendor/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/ExceptionListener.php line 190","context":{"exception":{"class":"Symfony\\Component\\HttpKernel\\Exception\\HttpException","message":"Missing value for required attribute \"commonName\"","code":0,"file":"/opt/stepup/Stepup-SelfService-3.1.0-20200123094957Z-899924d0139418958a9e502aa52eeea34494053d/vendor/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/ExceptionListener.php:190","previous":{"class":"Surfnet\\StepupSelfService\\SelfServiceBundle\\Exception\\MissingRequiredAttributeException","message":"Missing value for required attribute \"commonName\"","code":0,"file":"/opt/stepup/Stepup-SelfService-3.1.0-20200123094957Z-899924d0139418958a9e502aa52eeea34494053d/src/Surfnet/StepupSelfService/SelfServiceBundle/Security/Authentication/Provider/SamlProvider.php:122"}}},"extra":{"art":"32881","server":"sa.test.surfconext.nl","application":"self-service","request_id":"aa25f6bba864e2cfb7a9471687a2fea2"}}

But the user sees "Something went wrong; please try again" (see screenshot).
The user should be informed about the missing information.

Start with src/Surfnet/StepupSelfService/SelfServiceBundle/Security/Authentication/Provider/SamlProvider.php at line 122 and trace how MissingRequiredAttributeException reaches the user-facing error. Inspect the Symfony exception-handling path shown in the log. Done means the missing attribute information is presented to the user instead of only “Something went wrong; please try again.”