Pretty much everything is possible, but it depends on the amount of work required to achieve this. Managing access to the Event Manager using PHPBB groups is one of those situations that would require a lot of work. There is nothing built in to EPC to allow for that, so you'd have to code your own solution using PHPBB techniques - which we're not versed in.
As for hiding the username/password, you can send that info in POST instead of GET, but then the credentials would still be visible in the code.
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