code: def supply(self, issuer):
          
          issuer_uri_config = self._issuer_uri_configs.get(issuer)
  
          if not issuer_uri_config:
              # The issuer is unknown.
              return
  
          jwks_uri = issuer_uri_config.jwks_uri
          if jwks_uri:
              # When jwks_uri is set, return it directly.
              return jwks_uri
  
          # When jwksUri is empty, we try to retrieve it through the OpenID
          # discovery.
          open_id_valid = issuer_uri_config.open_id_valid
          if open_id_valid:
              discovered_jwks_uri = _discover_jwks_uri(issuer)
              self._issuer_uri_configs[issuer] = IssuerUriConfig(False,
                                                                 discovered_jwks_uri)
              return discovered_jwks_uri
docs: Supplies the `jwks_uri` for the given issuer.
  
          Args:
            issuer: the issuer.
  
          Returns:
            The `jwks_uri` that is either statically configured or retrieved via
            OpenId discovery. None is returned when the issuer is unknown or the
            OpenId discovery fails.