code: func (s *IdentityService) GetUserByOIDCIdentity(id services.ExternalIdentity) (services.User, error) {
  	users, err := s.GetUsers()
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	for _, u := range users {
  		for _, uid := range u.GetOIDCIdentities() {
  			if uid.Equals(&id) {
  				return u, nil
  			}
  		}
  	}
  	return nil, trace.NotFound("user with identity %q not found", &id)
  }
docs: // GetUserByOIDCIdentity returns a user by it's specified OIDC Identity, returns first
  // user specified with this identity