What is meaning of authentication "user context only" in subscription API

api

#1

I have seen the subscription API on
https://developer.twitter.com/en/docs/accounts-and-users/subscribe-account-activity/api-reference/new-subscription.

I have found the authentication is “user context only” but didn’t get it.

I have code in nodejs which is working fine, but I need code in PHP.

Can anyone help me how I can subscribe to my app by API in PHP.
https://api.twitter.com/1.1/account_activity/webhooks/:webhook_id/subscriptions.json