JavaScript-cross-domain login issues. For help.

I write a script on my own server, as long as the user access to this script, you can automatically login to such as SF's official website, log on the SF account password is the same, that is, if this person in the SF official website is not logged in the state, then just click on my script, the same as with my given account password login. After that, he simply clicks on the page in the browser, which is the user who has logged in.
Now facing a few problems
SF official website is no interface provided to me let me log in
I even grabbed the bag to simulate the SF's official website landing process, that cross-domain setting cookie how to solve?
Has anyone solved a similar problem? Asked for help.

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I write a script on my own server, as long as the user access to this script, you can automatically login to such as SF's official website, log on the SF account password is the same, that is, if this person in the SF official website is not logged in the state, then just click on my script, the same as with my given account password login. After that, he simply clicks on the page in the browser, which is the user who has logged in.
Now facing a few problems
SF official website is no interface provided to me let me log in
I even grabbed the bag to simulate the SF's official website landing process, that cross-domain setting cookie how to solve?
Has anyone solved a similar problem? Asked for help.

Using an IFRAME
But SF will verify. This is a Web security category.

Jsonp can also solve

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