code: @SuppressWarnings("unchecked")
    @Override
    public <T extends OAuth2AuthorizedClient> T loadAuthorizedClient(
        String clientRegistrationId, String principalName) {
      Assert.hasText(clientRegistrationId, "clientRegistrationId cannot be empty");
      Assert.hasText(principalName, "principalName cannot be empty");
      ClientRegistration registration =
          this.clientRegistrationRepository.findByRegistrationId(clientRegistrationId);
      if (registration == null) {
        return null;
      }
      return (T) this.authorizedClients.get(this.getIdentifier(registration, principalName));
    }
docs: Copy of {@link InMemoryOAuth2AuthorizedClientService#loadAuthorizedClient(String, String)}