Make function return initial user

dbms/src/Functions/currentUser.cpp

@@ -15,7 +15,7 @@ public:
     static constexpr auto name = "currentUser";
     static FunctionPtr create(const Context & context)
     {
-        return std::make_shared<FunctionCurrentUser>(context.getClientInfo().current_user);
+        return std::make_shared<FunctionCurrentUser>(context.getClientInfo().initial_user);
     }
 
     explicit FunctionCurrentUser(const String & user_name_) : user_name{user_name_}

dbms/tests/queries/0_stateless/00990_function_current_user.reference

@@ -1,3 +1,4 @@
 1
 1
+1	1
 1

dbms/tests/queries/0_stateless/00990_function_current_user.sql

@@ -1,4 +1,5 @@
 -- since actual user name is unknown, have to perform just smoke tests
 select currentUser() IS NOT NULL;
 select length(currentUser()) > 0;
-select currentUser() = user();
+select currentUser() = user(), currentUser() = USER();
+select currentUser() = initial_user from system.processes where query like '%$!@#%';

docs/en/query_language/functions/other_functions.md

@@ -103,7 +103,7 @@ Returns the name of the current database.
 You can use this function in table engine parameters in a CREATE TABLE query where you need to specify the database.
 
 ## currentUser()
-Returns the login of authorized user.
+Returns the login of authorized user (initiator of query execution).
 
 ## isFinite(x)