presto-main/src/main/java/io/prestosql/server/security/JsonWebTokenAuthenticator.java/JsonWebTokenAuthenticator/getKey
class JsonWebTokenAuthenticator:        public Key getKey(SignatureAlgorithm algorithm)
        {
            if (algorithm.isHmac()) {
                if (hmacKey == null) {
                    throw new UnsupportedJwtException(format("JWT is signed with %s, but no HMAC key is configured", algorithm));
                }
                return new SecretKeySpec(hmacKey, algorithm.getJcaName());
            }

            if (publicKey == null) {
                throw new UnsupportedJwtException(format("JWT is signed with %s, but no key is configured", algorithm));
            }
            return publicKey;
        }