presto-main/src/main/java/io/prestosql/server/security/JsonWebTokenAuthenticator.java/DynamicKeyLoader/DynamicKeyLoader
class DynamicKeyLoader:        public DynamicKeyLoader(String keyFile)
        {
            requireNonNull(keyFile, "keyFile is null");
            checkArgument(keyFile.contains(KEY_ID_VARIABLE));
            this.keyFile = keyFile;
        }