Cache Control and ETags

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A GET request on a resource will typically return a set of cache control headers. These include:

•	ETag: a unique identifier for the returned version of the resource

•	LastModified: the date/time when the resource was last modified.

These properties can then be used in subsequent calls to perform a conditional GET on the resource. By either:

•	Specifying the last retrieved ETag value for the resource in an If-None-Match request header or

•	Specifying the last retrieved LastModified value for the resource in an If-Modified-Since header

If the resource has not been modified, the server response will be a 304 Not Modified.