I want to insert new SP List items -- blog comments, to be exact -- on behalf of other users.
Ideally, I'd just pass a SharepointID for the user, but that doesn't seem to be possible. I think that Impersonation might be the most likely way to do this, but while I've found documentation on using user tokens for this within sharepoint applications, I haven't found a way to do this through the client object model.
Background: I'm writing a C# Windows Service that fetches email, parses it, and then inserts the contents as a comment on a given blog post. I'll only have the user's email address at first, but I can use that to grab their AD username, SharepointID, and presumably any other info I'd need to create the comment on their behalf -- except, of course, for their password.