The meat of the example

InventoryApiConnectionFactory.groovy

class InventoryApiConnectionFactory {

       // these properties would ordinarily be injected
       def authenticationProvider = new AuthenticationProvider()
       String username  = "username"
       String password  = "password"
       
       def logError(String msg) { println msg } // simulated logger

    def withInventoryConnection(Closure c) {
        def authenticatedUserToken = authenticationProvider.authenticateUser(username, password)
        def connection = new InventorySystem()
        def isOpen = connection.open(authenticatedUserToken)
        try {
            if(isOpen) {
                c.call(connection)
            }
        } catch (any) {
            logError("Something went wrong: ${any.message}".toString())
            throw any
        } finally {
            connection.close()
        }
       
    }

}