Thank you very much Angel, good explanation. 2. would be nice, but I read on the link you have provided for data source descriptor:
<user-name>sapdemo</user-name>
<password>sapdemo</password>
What I was looking for is a possibilty to use JPA on EP without providing any user credentials, nowhere. From my point of view the question if need to do it at all is more important than where you do it.
cheers