The joinery takes a bit of thinking when you have two beams meeting at a single post. The goal is to create a strong connection and avoid removing too much wood from the lumber. One solution is this corner joint with barrel bolts.
In this example we use barrel bolts and all-thread rod to tie everything together. One beam is fully seated on the post below with a stub tenon. This beam is cleverly notched so that the adjacent beam nestles into it and is seated on the post below. To secure this connection, a length of all-thread rod is drilled vertically into the post through the first beam and stub tenon, and then another length of rod is drilled horizontally through the two beams. Barrel bolts fasten all the parts together and make for an extremely strong assembly.