an fresh emerge of boinc 5.8.15 doesn't creates the gui_rpc_auth.cfg file, thus connection to localhost cant be established. can be worked around by emergeing boinc 5.4.11 and updating. Reproducible: Always
<snip> einfo "If you need to use the graphical client the password is in " einfo "/var/lib/boinc/gui_rpc_auth.cfg which is randomly generated " einfo "by BOINC upon successfully running the gui for the first time." einfo "You can change this to something more memorable." </snip> I don't exactly understand what's your problem. The client generates the password, not the ebuild.
(In reply to comment #1) einfo "If you need to use the graphical client the password is in " einfo "/var/lib/boinc/gui_rpc_auth.cfg which is randomly generated " einfo "by BOINC upon successfully running the gui for the first time." einfo "You can change this to something more memorable." the file isnt created, I was told that the ebuild is source of creating the file. if it isnt, then I apologize for the bug openning.