communicate with wordpress.com?

I use curl(PHP) to make a thing like proxy to
[myblog].wordpress.com

It’s work fine.
but i still have 1 problem.

other people on wordpress.com can’t comment my blog with their own account.

I see that I can comment other’s blog who use wordpress.com with domain like [myblog].com what’s the method that wordpress used to import account data cross domain?

I can’t use English fluently. I’m sorry for that.

??