Rate Limiting
Return a consistent response when a client exceeds their quota.
If your site requires some form of rate limiting, you must return a consistent
response when a client exceeds their quota. This response must use the 429 status code defined
in RFC 6585 Section 4, as well
as the Retry-After header defined
in RFC 7231 Section 7.1.3.
The Retry-After header should be set to the time at which the client can retry the request, using
the http-date type instead of the delta-seconds type.
For purpose of browser-level caching, the server may also include the Vary header.
HTTP/1.1 429 Too Many Requests
Retry-After: Mon, 01 Jan 2018 00:00:00 GMT
Vary: Origin, Authorization