public static String getIssuer(final String token) {
        DecodedJWT jwt = JWT.decode(token);
        return Optional.of(jwt).map(item -> item.getClaim("userName").asString()).orElse("");
    }
according to token to get issuer.

@param token token
@return Issuer {@link String}
shenyu-admin/src/main/java/org/apache/shenyu/admin/utils/JwtUtils.java