Support oauth2 token caching

[sbuettner]

Is your feature request related to a problem? Please describe.

As discussed in this forum thread the http outbound connector is issuing a new token for every request. This can lead to a high amount of token issue request on the customer side which can be prevented by caching the generated token for a configured amount of time.

Describe the solution you'd like

The http outbound connector should support caching of token to re-use previously issued tokens when creating outbound requests.

Tasks

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1. Add an in-memory token cache to the http outbound connector based on caffeine

[geemov42]

Hello,
I understand the problematic but I see the things in an alternative way that let us do what we want concerning the http request security.
When we look, rest and soap are based on http but need different kind of security. To do the job I have modified some class to support the security delegation to an external component like spring security.
With this modification I can let spring security manage the tokens (because you could have multiple client registration).

You can find the intellij path in attachment :
add_the_possibility_to_use_an_external_component_to_secure_a_request.patch