Key based authorization for programmatic clients is described. One or more server computers receive a request for an action on one or more target resources, the request indicating the action to be performed on the one or more target resources at the resource access point, and a key identifying a client program running on a client computer system. A data store that stores mapping data representing one or more associations among keys, actions and target resources is queried. An existence, in the data store, of an association of a particular key corresponding to a particular client program, with a particular target resource and with a particular action associated with the particular target, represents the particular client program having authorization to perform the particular action on the particular target resource. The system authorizes performance of the action on the one or more target resources for the request.