Add deprecations for OAuth2.

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignAutoConfiguration.java

@@ -312,6 +312,7 @@ public class FeignAutoConfiguration {
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(OAuth2ClientContext.class)
 	@ConditionalOnProperty("feign.oauth2.enabled")
+	@Deprecated // spring-security-oauth2 reached EOL
 	protected static class Oauth2FeignConfiguration {
 
 		@Bean

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/security/OAuth2FeignRequestInterceptor.java

@@ -43,6 +43,7 @@ import org.springframework.security.oauth2.common.OAuth2AccessToken;
  * @author Tim Ysewyn
  * @since 3.0.0
  */
+@Deprecated // spring-security-oauth2 reached EOL
 public class OAuth2FeignRequestInterceptor implements RequestInterceptor {
 
 	/**