Where does the authorial voice come into the text and what is the voice saying in Hamlet?

Concerning authorial voice or intrusion into the text of
Shakespeare's Hamlet, I'm afraid you're pretty much out of luck. 
Hamlet is a play, not a work of fiction or narrative poetry.  Every
word spoken is spoken by a character, not by the author.  Therefore, no authorial voice
exists in the play. 

There's not even a chorus that one
might suggest provides authorial intrusion.

I'm afraid the
best you may be able to do is to point to the advice the character Hamlet gives to the
Players about acting, after they arrive in Elsinore.  Some commentators have seen
Shakespeare's advice in Hamlet's advice.  Even this, though, is speculation, and the
text is still technically dialogue spoken by a character, not authorial
intrusion.