Make OAuth2Error Serializable

Fixes gh-4944

oauth2/oauth2-core/src/main/java/org/springframework/security/oauth2/core/OAuth2Error.java

@@ -15,8 +15,11 @@
  */
 package org.springframework.security.oauth2.core;
 
+import org.springframework.security.core.SpringSecurityCoreVersion;
 import org.springframework.util.Assert;
 
+import java.io.Serializable;
+
 /**
  * A representation of an <i>OAuth 2.0 Error</i>.
  *
@@ -30,7 +33,8 @@ import org.springframework.util.Assert;
  * @since 5.0
  * @see <a target="_blank" href="https://tools.ietf.org/html/rfc6749#section-11.4">Section 11.4 OAuth Extensions Error Registry</a>
  */
-public final class OAuth2Error {
+public final class OAuth2Error implements Serializable {
+	private static final long serialVersionUID = SpringSecurityCoreVersion.SERIAL_VERSION_UID;
 	private final String errorCode;
 	private final String description;
 	private final String uri;