{ 'email': ,
  <arbitrary metadata: name, birthday, address, favorite ice cream, etc>
  'password': 'secret',
  
}

# you sign in with an email address
# email addresses should be multiple

def Member(object):

    def role(self, discussion):
        """
        member's role with respect to discussion or conference;
        returns 'admin', 'member', or None
        """

    def add(self, discussion):
        """adds a member to a discussion"""