Email templating: URL construction for links unpurposeful, leads to information disclosure in some cases

[jane-heller-bkg]

The URL for links that are presented to the user, eg. to activate accounts is based on the internal variable mail.smtp.host, which the application uses to contact its mailserver to deliver the email. That does not make sense.

Some of the URLs are generated in sources/Re3gistry2/src/main/java/eu/europa/ec/re3gistry2/web/controller/RegistryManagerUsersAdd.java:246 (as of commit 41ce0d21d146c0af344ec873977dbc02aeb07aea) and following line.
URL needs to be created following a fixed scheme, eg. derived out of a single variable in the configuration. Software seems to handle URL generation arbitrarily at the moment, see also e.g. #438, #367

This is also a security issue because it leads to an information disclosure about internal contact addresses of mailservers.