One of the titles of St. Jospeh is, “Most Just,” or San Giuseppe, Giustissimo.
One source for this is the Gospel reading for the Third Thursday in Advent. Here is the NAB version used in the American lectionary:
This is how the birth of Jesus Christ came about.
When his mother Mary was betrothed to Joseph,
but before they lived together,
she was found with child through the Holy Spirit.
Joseph her husband, since he was a righteous man,
yet unwilling to expose her to shame,
decided to divorce her quietly.
Such was his intention when, behold,
the angel of the Lord appeared to him in a dream and said,
“Joseph, son of David,
do not be afraid to take Mary your wife into your home.
For it is through the Holy Spirit
that this child has been conceived in her.
She will bear a son and you are to name him Jesus,
because he will save his people from their sins.”
All this took place to fulfill
what the Lord had said through the prophet:Behold, the virgin shall be with child and bear a son,
and they shall name him Emmanuel,which means “God is with us.”
When Joseph awoke,
he did as the angel of the Lord had commanded him
and took his wife into his home.
He had no relations with her until she bore a son,
and he named him Jesus.
The first reading for this day (Jeremiah 23:5-8), as well as the Psalm (Ps. 72:1-2, 12-13, 18-19), speak also of God’s justice.