Our auto-configuration for RestTemplateBuilder provides a RestTemplateBuilderConfigurer to easily apply Boot's defaults when defining a custom RestTemplateBuilder. Would should consider an equivalent for RestClient.Builder, although we only apply RestClientCustomizer beans to the builder at the moment so the need for it doesn't appear to be that large.
Comment From: mhalbritter
There's now a RestClientBuilderConfigurer which can be used to apply Boots defaults to RestClient.Builders.