[MSSQL] restricting logins to SQL Server, or limiting the number of sessions for a specific login

For example, in the following code, the logon trigger denies log in attempts to SQL Server initiated by login login_test if there are already three user sessions created by that login.

USE master;  
GO  
CREATE LOGIN login_test WITH PASSWORD = '3KHJ6dhx(0xVYsdf' MUST_CHANGE,  
    CHECK_EXPIRATION = ON;  
GO  
GRANT VIEW SERVER STATE TO login_test;  
GO  
CREATE TRIGGER connection_limit_trigger  
ON ALL SERVER WITH EXECUTE AS 'login_test'  
FOR LOGON  
AS  
BEGIN  
IF ORIGINAL_LOGIN()= 'login_test' AND  
    (SELECT COUNT(*) FROM sys.dm_exec_sessions  
            WHERE is_user_process = 1 AND  
                original_login_name = 'login_test') > 3  
    ROLLBACK;  

END;  

https://docs.microsoft.com/en-us/sql/relational-databases/triggers/logon-triggers?view=sql-server-2017