Safely securing a 4x4 vertically and horizontally
This can take a load of 1,950/1.6=1,289 pounds. Just make sure the cantilever length doesn't exceed it's back span. Make sure there's 2 installed on each post to beam connection.

For the horizontal force, install (1) Simpson A21 on the underside of the beam to the side of the post on the left and (2) Simpson A21 from the underside of the beam to the faces of the post on the right. Use (2) 0.148 x 1 1/2 nails for each of the clip connections.