Could you please explain what are you trying to achieve and give some more details.
Usually <vcenter_ip>/ui is used to access the HTML Client and <vcenter_ip>/vsphere-client is used to acces the Flex Client.
I want to call check valid login with usrid & password as parameter/ arguments.
or using header params in case post request
which can return me with vallid http status and json data with details.
If i use flex/ html not sure how can i check same.
You can get the current user session by using the UserSessionService's getUserSession() method. It will give you information about the currently logged in user or null otherwise.