def userid_from_username(username, request):
    """Return the full user ID for the given username.

    For example for username "seanh" return "acct:seanh@hypothes.is"
    (if we're at domain "hypothes.is").

    """
    return u"acct:{username}@{domain}".format(username=username,
                                              domain=request.auth_domain)