Use http cache for improving performance

[int128]

Use the http cache to reduce time for the OIDC discovery. See https://github.com/kubernetes/client-go/blob/790a4f63632139cf6731014d00a9a8338f1fbd7d/discovery/cached/disk/round_tripper.go.

[int128]

Keycloak does not allow cache:

% curl -v -L https://keycloak.example.com/auth/realms/hello/.well-known/openid-configuration
> GET /auth/realms/hello/.well-known/openid-configuration HTTP/2
> Host: keycloak.example.com
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/2 200
< date: Mon, 24 Jun 2019 13:45:18 GMT
< content-type: application/json
< content-length: 2421
< vary: Accept-Encoding
< cache-control: no-cache, must-revalidate, no-transform, no-store

Google IdP allows cache:

% curl -v -L https://accounts.google.com/.well-known/openid-configuration
> GET /.well-known/openid-configuration HTTP/2
> Host: accounts.google.com
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/2 200
< accept-ranges: none
< vary: Accept-Encoding
< content-type: application/json
< access-control-allow-origin: *
< date: Mon, 24 Jun 2019 13:04:19 GMT
< expires: Mon, 24 Jun 2019 14:04:19 GMT
< last-modified: Mon, 05 Nov 2018 17:08:01 GMT
< x-content-type-options: nosniff
< server: sffe
< x-xss-protection: 0
< age: 1893
< cache-control: public, max-age=3600
< alt-svc: quic=":443"; ma=2592000; v="46,44,43,39"

[int128]

kubelogin validates the token without the discovery and cache is not needed now. Close.