Windows: Unify OCI user struct

Signed-off-by: John Howard <jhoward@microsoft.com>

daemon/oci_windows.go

@@ -72,7 +72,7 @@ func (daemon *Daemon) createSpec(c *container.Container) (*libcontainerd.Spec, e
 	s.Process.Env = c.CreateDaemonEnvironment(linkedEnv)
 	s.Process.InitialConsoleSize = c.HostConfig.ConsoleSize
 	s.Process.Terminal = c.Config.Tty
-	s.Process.User.User = c.Config.User
+	s.Process.User.Username = c.Config.User
 
 	// In spec.Root
 	s.Root.Path = c.BaseFS

libcontainerd/windowsoci/oci_windows.go

@@ -66,9 +66,16 @@ type Process struct {
 	Cwd string `json:"cwd"`
 }
 
-// User contains the user information for Windows
+// User specifies specific user (and group) information for the container process.
 type User struct {
-	User string `json:"user,omitempty"`
+	// UID is the user id.
+	UID uint32 `json:"uid" platform:"linux,solaris"`
+	// GID is the group id.
+	GID uint32 `json:"gid" platform:"linux,solaris"`
+	// AdditionalGids are additional group ids set for the container's process.
+	AdditionalGids []uint32 `json:"additionalGids,omitempty" platform:"linux,solaris"`
+	// Username is the user name.
+	Username string `json:"username,omitempty" platform:"windows"`
 }
 
 // Root contains information about the container's root filesystem on the host.