Why does Finder need me to authenticate its every action?
Sounds like a permissions issue.

Press Command+I while the highest level folder you want to be able to access.  At the bottom of the info dialog, be sure the lock is unlocked.  If the user name you wish to access the files from is in the list, be sure it is set to Read &amp; Write.  If it is not in the list, press the plus sign at the bottom of the dialog.  In the dialog that opens, select the user name you wish to access the files from and press OK.  Then, be sure that this user has Read &amp; Write access.  

If this doesn't solve your issue, please let me know.