I've been assigned as an anonymous referee to review a paper submitted to a prestigious journal by coworkers of a friend of mine and have told him about it without mentioning the authors' names. My friend's reaction was "wow," and he is now pushing me to reveal to him whose paper I am refereeing. The department at which he works is large, so he can't really make a good guess on his own. He says that he knows all his coworkers at the department personally and would really love to use this unique opportunity to help establish a connection between me and them.
Of course, I'd love to chat with them about their research and expand my connections, especially as one of the authors is a well-known professor, but I'm unsure whether it's okay to let the authors know, through my friend, that I am a referee of their paper. I've seen no policy against this, but I'm afraid it might be just not okay.
As an early-career researcher I'd really appreciate any input from users of this SE as to how to navigate this situation.
Additional info: While I like the paper, it is clearly not acceptable to this high-profile journal, and I have to write that in my review. The first author is a young postdoc, and he obviously just tried his luck with this journal. So, there is no way that the relationship with my friend or any possible contact with the authors can affect my recommendation regarding this paper.
Update 2: The answers strongly suggest that revealing my identity as a reviewer is a terrible idea. What about doing this after the editor makes a final decision about the paper? Would it be okay at that point?
Update 3: After reading the answers and the comments, I told my friend I can't reveal any further information or get engaged in any contact with the authors in the context of refereeing the paper. Thanks everyone for helping me choose the right thing to do.