How to check whether a user is logged in through logon group or directly?
 
Solution:
 
This can be catch during logon time. 
 
I remember at the times of the old OSS - when you tried to logon directly to one of the application servers - you got the error message:  "Please don't use a direct logon but rather the group logon - and you got logged of."
 
There's a user exit for that:
 
Note 37724 - Customer exits in SAP logon.
 
You may be able to modify the exit according to suit your needs.
 
Note 609863 - How to lock out users using GUIs of wrong version.
 
Here's some example code where you can create a table whose users may directly logon to application servers. All others are kicked out:
 
*DATA: it_zsbc_lm_config LIKE zsbc_lm_config OCCURS 1,
* wa_zsbc_lm_config LIKE LINE OF it_zsbc_lm_config,
* it_logondata TYPE bapilogond,
* it_return TYPE STANDARD TABLE OF bapiret2 WITH HEADER LINE,
* bapi_username TYPE xubname,
* can_logon TYPE c,
* errmessage(128) TYPE c.
*
*can_logon = ‘N’.
*
*SELECT
* *
*FROM
* zsbc_lm_config
*INTO TABLE
* it_zsbc_lm_config
*WHERE
* server = sy-host.
*IF sy-subrc = 0.
* “At this point, we know that a logon group restriction has been
* “entered for this server
* bapi_username = sy-uname.
* CALL FUNCTION ‘BAPI_USER_GET_DETAIL’
* EXPORTING
* username = bapi_username
* IMPORTING
* logondata = it_logondata
* TABLES
* return = it_return.
* LOOP AT it_zsbc_lm_config INTO wa_zsbc_lm_config.
* IF wa_zsbc_lm_config-ugroup = it_logondata-class.
* can_logon = ‘Y’.
* ENDIF.
* ENDLOOP.
* IF can_logon = ‘N’.
* CONCATENATE
* ‘You are not authorized to log on to this server. Please’
* ‘choose a different server.’
* INTO
* errmessage
* SEPARATED BY
* space.
* CALL FUNCTION ‘POPUP_TO_INFORM’
* EXPORTING
* titel = ‘ERROR!’
* txt1 = errmessage
* txt2 = ‘You will now be logged off.’.
*
* CALL ‘SYST_LOGOFF’.
* ENDIF.
*
*ENDIF.

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