In many cases many people needs authoring in common blog. For that case web admin have to create a blog which is owned by "group" (not by web user) and then granting this role to users which are authors will give them access to post on that blog. As group cannot be authenticated, thus it's not possible to login as group and post on behalf of it; the post's author have to be a valid web user account. This feature does not contradict with possibility authors to have their own blogs, they can have own and post to many "group" blogs. Granting access to a "group" blog can be done via WebDAV users UI, or with GRANT statement via ISQL tool.