Some APIs have resources where a POST is used to send a command that returns
content and doesn't modify state. In this case, it's more like a GET. This
may occur where one might normally GET but the request URI would be too long
for the server to accept. cachedPOST thus behaves more like
GET, checking for a cached response before performing the request and
setting cache if the request is successful. It does no cache dropping, unlike
POST().
cachedPOST(url, ...)character URL of the request
additional arguments passed to the httr functions
The corresponding httr response object, potentially read from cache