Separate TokenRefresh capability from ServerOAuth2AuthorizedClientExchangeFilterFunction

[wtatum]

Summary

The ability to automatically and transparently refresh an OAuth 2 token in ServerOAuth2AuthorizedClientExchangeFilterFunction is useful enough that I'd like to be able to use it in other places. However most of the "meat" of the class is private. My particular case is an attempt to solve and/or work around spring-attic/spring-cloud-security#175 by implementing a refresh using the logic provided in ServerOAuth2AuthorizedClientExchangeFilterFunction. Unfortunately the interface of ServerOAuth2AuthorizedClientExchangeFilterFunction is specific to ClientRequest / ClientResponse and the interface of Spring Cloud Gateway's GatewayFilter is specific to ServerWebExchange.

A lot of the internals of ServerOAuth2AuthorizedClientExchangeFilterFunction are about retrieving and updating the OAuth2AuthorizedClient, and would be equally applicble to ClientRequest or ServerWebExchange, with only a little bit of glue needed to adapt to the right interface.

Actual Behavior

Otherwise reusable behaviors of ServerOAuth2AuthorizedClientExchangeFilterFunction are implemented in private methods.

Expected Behavior

The more reusable methods such as refreshIfNecessary (and dependencies) should be extracted to utility functions or a more reusable bean.

[jgrandja]

@wtatum This work is currently underway in #6811. One of the tasks includes separating the refresh_token logic into a new implementation of OAuth2AuthorizeClientProvider to allow for reuse.

I'm going to close this issue as a duplicate.