security.clear_api_key_cache does not document all routes.

[Mpdreamz]

The tests for security.clear_api_key_cache seems to indicate that ids is optional by allowing to pass an empty string "" for ids.

https://github.com/elastic/elasticsearch/blob/7.10/x-pack/plugin/src/test/resources/rest-api-spec/test/api_key/10_basic.yml#L197-L198

And therefor the tests assumes whatever builds the url will happily build /_security/api_key//_clear_cache.

This is true for the java test runner but this is not true for the more strict clients.

The spec and the RestAction need to explictly define /_security/api_key/_clear_cache as a valid route to clear all API's.

After a quick peek I suspect the same is true for several other security related (clear_*) API's

[elasticmachine]

Pinging @elastic/es-security (:Security/Authentication)

[ywangd]

Hi @Mpdreamz as you have noticed, the double slash pattern was added there following existing pattern in the code. @albertzaharovits and I did have brief discussion about adding support for the single slash version. But we haven't come to a conclusion yet. Let me discuss this with the team and come back to you.