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Is there a way to determine whether the logged in User is a proxy?
The Admin can login to another users account using a proxy.
Is there a way using Apex or any other Salesforce feature to find whether the logged in User is proxy or not?
I'm not sure what you mean. An Admin can only log in to a user's account in the following ways:
1) User grants Login As access to their Admin
2) User gives Admin their username/password (bad practice)
3) Admin changes user's email address and resets their password
To log in as a user through a proxy, an Admin would need to force the user's network traffic through the proxy, break the SSL tunnel, then wait for the user to log in to Salesforce and steal their password or Session Id. If this were happening, the user should get browser warnings that the website they are connecting to uses an incorrect SSL certificate. In both IE and Firefox this is a big warning screen that the user must acknowledge before the connection continues.
I mean,
When user grants login permission to Admin and then if Admin logs in to that persons account, is there a way to find whether the logged in user is Admin.
Can we find that using Apex or is there any other way to find that?