I find this on official doc for client ID :
During your initial setup you will need to contact Valve with the following information: What permissions you need the user to obtain. The required permissions are listed below with each API call. The token lifetime. The redirect URI to send the user back to after completing authentication/authorization. In return, Valve will assign a Client ID for your implementation.
But they didn't mention how to contact valve for the same. I found many same questions on different platform but can't find any solution to this.
I am little confuse in steam-ID and Client-ID. Are they the same? if not then how to retrive client-id from valve.
Sorry If i miss anything here
Answering my own question for someone's reference.
O-auth is not supported in stream any more, But official documentation is still there which is useless right now.
Need to implement it using Open-ID which is the only solution.
There are many PHP and other language's reference on git-hub.
If anyone need any help feel free to ask here i have implemented it successfully.
And also client-id and steam-Id are not same.