[TASK] check if openididentifier exists before emtit external call

[samamedick]

When authentication with an openid identifier is processed a request to an external system is made. In the current implementation there is no check, if the identifier is valid for the system.

This can misslead to a identified server side request forgery when doing a securtity scan on typo3 instances with enabled openid. It would be not easy or not possible to do a attack this way, but the effect is not nice.

To validate the problem:

• open a typo3 backend login with enabled openid
• add an fqdn of a website where you habe access to logs into the openid field
• press login
• check logs for calls like "GET / HTTP/1.1" 301 536 "-" "php-openid/2.2.2 (php/7.4.30) curl/7.64.0"

Content of this pull request solves the problem.