(US) Options Assignment

How does option assignment work in terms of taxation from a FOREIGN BROKERAGE in Japan?

For example, sell a put, collect $100 of premium from the sale. The option gets assigned and I pay $1000 for the stock.

Do I get to roll the PUT OPTION premium into the price of and pay tax later when I sell it (like a Japanese brokerage) or do I have to pay tax the the year the option was assigned? For a pure option play, I would calculate tax at the time of buying it back or expiration, but this involved assignment.

Keeping it mind it's a US brokerage:

Do I pay tax on $100 when it's assigned?

Or

Do I pay tax when I sell the stock?

Thanks in advance!

by No_Garage_4558