Javascript-Cross-Origin login problems. Help

I write a script on my server. as long as the user accesses this script, the user can automatically log on to the official sf website, for example. the login password of the sf account is the same, that is to say, if this person is not logged on to the official sf website, just click my script, it is the same as using my account... I write a script on my server. as long as the user accesses this script, the user can automatically log on to the official sf website, for example. the login password of the sf account is the same, that is to say, if this person is not logged on to the official sf website, you just need to click my script, which is the same as logging on with the account password you have given. Then, as long as he clicks the page in the browser, all of them are in the login status.
Several problems
No interface is provided on the official sf website for me to log on.
Even if I capture packets to simulate the login process on the official sf website, how can I solve cross-domain cookie setting?
Has anyone solved similar problems? Help.

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I write a script on my server. as long as the user accesses this script, the user can automatically log on to the official sf website, for example. the login password of the sf account is the same, that is to say, if this person is not logged on to the official sf website, you just need to click my script, which is the same as logging on with the account password you have given. Then, as long as he clicks the page in the browser, all of them are in the login status.
Several problems
No interface is provided on the official sf website for me to log on.
Even if I capture packets to simulate the login process on the official sf website, how can I solve cross-domain cookie setting?
Has anyone solved similar problems? Help.

Use iframe
However, sf will verify. This is a part of web security.

Jsonp can also solve