code: protected JsonWebKey getJsonWebKeyForEncryption(final OidcRegisteredService svc) {
          LOGGER.debug("Service [{}] is set to encrypt tokens", svc);
          val jwks = this.serviceJsonWebKeystoreCache.get(svc);
          if (Objects.requireNonNull(jwks).isEmpty()) {
              throw new IllegalArgumentException("Service " + svc.getServiceId()
                  + " with client id " + svc.getClientId()
                  + " is configured to encrypt tokens, yet no JSON web key is available");
          }
          val jsonWebKey = jwks.get();
          LOGGER.debug("Found JSON web key to encrypt the token: [{}]", jsonWebKey);
          if (jsonWebKey.getPublicKey() == null) {
              throw new IllegalArgumentException("JSON web key used to sign the token has no associated public key");
          }
          return jsonWebKey;
      }
docs: Gets json web key for encryption.
  
  @param svc the svc
  @return the json web key for encryption