I need to support legacy API, which have constant url and request is differentiate using xml body. Is there any option to use body as cache KEY in Google CDN?
If no, I'm thinking about rewriting requests to add based64 body in url, what do you think about that?
No, Google Cloud CDN does not support using the request body as part of the cache key. Moving the relevant information to the URL would work, but only if the HTTP method is GET or HEAD. (Google Cloud CDN never serves cached content in response to other HTTP methods such as POST.)
There's more information on cache keys at https://cloud.google.com/cdn/docs/caching#cache-keys.
