Single terminal login

[<stevenr () mastek com>]

Hi

I have worked with web based applications since quite some time. One issue to which I have not found a satisfactory 
answer yet is that of a problem with Single Terminal Login in a web based application. 

By Single Terminal Login, I mean that if one user logs into a web application (say JSP based), s/he should not be able 
to login from another machine or even another browser from the same machine. This can be achieved easily by setting a 
"logged in" flag on the server side using a DB or LDAP etc. When the user clicks on the Logout link, the flag is reset 
and only then the user can login from another browser/window. Now the hitch. If the user closes the browser directly, 
or the power goes out, or browser hangs and has to be killed, the flag remains as "logged in". In short user cannot 
login into the system again. The one workaround used commonly, is setting a timeout after which the user can login 
again, where a "last active time" is maintained for each user. Every login request is cross-checked against this time 
and if the difference is greater than some threshold value, the user is able to login again.  But this means that 
everytime the user does something the "last active time" will have to be updated, which will be expensive in a high 
traffic site. Also, the threshold value is always a hot topic of debate :-)

Does anyone know a better or a different approach to this? Would be helpful if someone knows some site/papers for this. 
Have googled but havent come across any myself.

- Steve

"He who laughs last probably made a backup..." 



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