1. A computer-implemented method of session management for controlling video delivery to a client device over a network, the computer-implemented method comprising: receiving, at a server, a request from a client device to access video content; accessing a data file that defines a workflow sequence to execute via a workflow engine, the workflow sequence defining multiple nodes, each node identifying at least one session management service to execute, wherein at least one node identifies data passed between given session management services, and wherein a new session management service can be added to the workflow sequence without interrupting service to the client device; loading the workflow sequence and multiple nodes into a shared memory; executing, via the workflow engine, session management services corresponding to the multiple nodes according to the workflow sequence; and transmitting instructions to a remote headend to transmit the video content to the client device.