Using

force: true, skip_nil: true

does not work the way you described it in:

Our #fetch_jwks method only returns the JSON response if the request was successful, and nil otherwise. Meaning we can cater for any failed response by leaving the current value in the cache, so we always have the latest successful response we've received.

The cache will be cleared even if the response is not successful and fetch_jwks returns nil.

Rails.cache.fetch("JWKS_CACHE_KEY", force: true, skip_nil: true) do
  Time.now.to_s  
end  
=> "2021-08-31 11:22:32 +0200"

Rails.cache.fetch("JWKS_CACHE_KEY", force: true, skip_nil: true) do
  nil  
end  
=> nil

Rails.cache.fetch("JWKS_CACHE_KEY")
=> nil