https://cloud.spring.io/spring-cloud-netflix/multi/multi_spring-cloud-feign.html

OAuth2FeignRequestInterceptor 
https://github.com/spring-cloud/spring-cloud-security/blob/master/spring-cloud-security/src/main/java/org/springframework/cloud/security/oauth2/client/feign/OAuth2FeignRequestInterceptor.java
    https://javadoc.io/doc/org.springframework.cloud/spring-cloud-security/latest/org/springframework/cloud/security/oauth2/client/feign/OAuth2FeignRequestInterceptor.html

cfg
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/client/resource/OAuth2ProtectedResourceDetails.html

baeldung
https://www.baeldung.com/spring-cloud-feign-oauth-token
2017
https://stackoverflow.com/questions/45859676/spring-cloud-feign-oauth2-request-interceptor-is-not-working

issues
https://github.com/spring-cloud/spring-cloud-security/issues/173
    https://github.com/loesak/spring-cloud-security-173
    https://github.com/oktadeveloper/java-microservices-examples/blob/master/spring-boot+cloud/api-gateway/src/main/java/com/example/apigateway/UserFeignClientInterceptor.java
artem
    https://github.com/spring-cloud/spring-cloud-security/issues/220