[#158] client: Support object context in session token setter

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

session/session.go

@@ -200,7 +200,8 @@ func (t *Token) Signature() *signature.Signature {
 // SetContext sets context of the Token.
 //
 // Supported contexts:
-//  - *ContainerContext.
+//  - *ContainerContext,
+//  - *ObjectContext.
 //
 // Resets context if it is not supported.
 func (t *Token) SetContext(v interface{}) {
@@ -209,6 +210,8 @@ func (t *Token) SetContext(v interface{}) {
 	switch c := v.(type) {
 	case *ContainerContext:
 		cV2 = c.ToV2()
+	case *ObjectContext:
+		cV2 = c.ToV2()
 	}
 
 	t.setBodyField(func(body *session.TokenBody) {