code: func (m UsersAPIAuthMethod) Authenticate(c context.Context, r *http.Request) (*auth.User, error) {
  	u := user.Current(c)
  	if u == nil {
  		return nil, nil
  	}
  	id, err := identity.MakeIdentity("user:" + u.Email)
  	if err != nil {
  		return nil, err
  	}
  	return &auth.User{
  		Identity:  id,
  		Superuser: u.Admin,
  		Email:     u.Email,
  	}, nil
  }
docs: // Authenticate extracts peer's identity from the incoming request.