https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/client/OAuth2RestTemplate.html

cfg
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/client/token/grant/client/ClientCredentialsAccessTokenProvider.html
    https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/client/token/OAuth2AccessTokenSupport.html
https://stackoverflow.com/questions/27864295/how-to-use-oauth2resttemplate

2019
https://www.baeldung.com/spring-security-oauth2-authentication-with-reddit

samples
https://github.com/mariubog/oauth-client-sample