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

AuthServer

endpoints
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/provider/endpoint/package-summary.html
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/provider/endpoint/CheckTokenEndpoint.html
    /oauth/check_token
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/provider/endpoint/TokenKeyEndpoint.html
    /oauth/token_key


AuthClient

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

    OAuth2RestTemplate
    https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/client/OAuth2RestTemplate.html
    https://github.com/spring-projects/spring-security-oauth/blob/master/spring-security-oauth2/src/main/java/org/springframework/security/oauth2/client/OAuth2RestTemplate.java
    https://stackoverflow.com/questions/27864295/how-to-use-oauth2resttemplate

    grant types
    org.springframework.security.oauth2.client.token.grant.code.AuthorizationCodeResourceDetails
    org.springframework.security.oauth2.client.token.grant.client.ClientCredentialsResourceDetails;

AuthProvider

https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/provider/package-summary.html

    CommonOAuth2Provider
    https://github.com/spring-projects/spring-security/blob/master/config/src/main/java/org/springframework/security/config/oauth2/client/CommonOAuth2Provider.java

config.annotation
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/config/annotation/
config.xml
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/config/xml/package-summary.html

common
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/common/package-summary.html

expiration
ExpiringOAuth2RefreshToken
https://docs.spring.io/spring-security/oauth/apidocs/org/springframework/security/oauth2/common/ExpiringOAuth2RefreshToken.html
    protected boolean isExpired(OAuth2RefreshToken refreshToken) {
        if (refreshToken instanceof ExpiringOAuth2RefreshToken) {
            ExpiringOAuth2RefreshToken expiringToken = (ExpiringOAuth2RefreshToken) refreshToken;
            return expiringToken.getExpiration() == null
                || System.currentTimeMillis() > expiringToken.getExpiration().getTime();
        }
        return false;
    }