ORIGINAL_LOGIN (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns the name of the login that connected to the instance of SQL Server. You can use this function to return the identity of the original login in sessions in which there are many explicit or implicit context switches.
Transact-SQL syntax conventions
Syntax
ORIGINAL_LOGIN( )
Return Types
sysname
Remarks
This function can be useful in auditing the identity of the original connecting context. Whereas functions such as SESSION_USER and CURRENT_USER return the current executing context, ORIGINAL_LOGIN returns the identity of the login that first connected to the instance of SQL Server in that session.
Examples
The following example switches the execution context of the current session from the caller of the statements to login1. The functions SUSER_SNAME and ORIGINAL_LOGIN are used to return the current session user (the user to whom the context was switched), and the original login account.
Note
Although the ORIGINAL_LOGIN function is supported on Azure SQL Database, the following script will fail because Execute as LOGIN is not supported on Azure SQL Database.
USE AdventureWorks2022;
GO
--Create a temporary login and user.
CREATE LOGIN login1 WITH PASSWORD = 'J345#$)thb';
CREATE USER user1 FOR LOGIN login1;
GO
--Execute a context switch to the temporary login account.
DECLARE @original_login sysname;
DECLARE @current_context sysname;
EXECUTE AS LOGIN = 'login1';
SET @original_login = ORIGINAL_LOGIN();
SET @current_context = SUSER_SNAME();
SELECT 'The current executing context is: '+ @current_context;
SELECT 'The original login in this session was: '+ @original_login
GO
-- Return to the original execution context
-- and remove the temporary principal.
REVERT;
GO
DROP LOGIN login1;
DROP USER user1;
GO