What is Impersonation why do you use it and how does SQL per

What is Impersonation, why do you use it and how does SQL perform implicit Impersonation?

Solution

Impersonation is an arrangement in which an SQL Server is configured to allow an instance of one SQL server to connect to another instance of SQL server under the context of an autenticated Windows User.

Impersonation can be done explicitly or implicitly on a SQL server.
The EXECUTE AS statement is used to do explicity Impersonation, It can be used to impersonate server-level,database-level principals on logins, users.
implicit Impersonation is on modules(server-level,database-level)
database-level -> stored procedure , function
server-level -> server-level trigger.

The EXECUTE AS CALLER will change the context to the caller\'s context, this change does not revert to the implicitly impersonated context,
REVERT should be called to get back to previous context.
EXECUTE AS CALLER does not require any permission check.
Based on the triggers the implicit impersonation is called directly.