1. A method of admission control for admitting global and application session requests in a grid computing system, the method comprising: receiving a user request for a global session from a user at a submission node, wherein the submission node includes a computing system local to the user; receiving from the user a list of applications to be launched through the global session; identifying the applications as a set of allowed applications by consulting authorization policies specifying a list of allowed applications; determining resource requirements for the identified applications; allocating an execution node satisfying the resource requirements, wherein the allocated execution node includes a computing system remote from the user; establishing the global session between the allocated execution node and the submission node, wherein the global session creates a network connection between the submission node and the allocated execution node allowing the submission node to utilize resources associated with the allocated execution node; receiving a user request for an application session through the established global session; and establishing the application session with the allocated execution node, wherein the application session allows the user to interact directly with one or more applications running on the execution node.