Transient Authentication Tokens

This commit introduces support for transient authentication tokens
which indicate to the filter chain, specifically the
HttpSessionSecurityContextRepository, whether or not the token ought
to be persisted across requests.

To leverage this, simply annotate any Authentication implementation
with @TransientAuthentication, extend from an Authentication that uses
this annotation, or annotate a custom annotation.

Implementations of SecurityContextRepository may choose to not persist
tokens that are marked with @TransientAuthentication in the same way
that HttpSessionSecurityContextRepository does.

Fixes: gh-5481

core/src/main/java/org/springframework/security/core/TransientAuthentication.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2002-2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.security.core;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * A marker for {@link Authentication}s that should never be stored across requests, for example
+ * a bearer token authentication
+ *
+ * @author Josh Cummings
+ * @since 5.1
+ */
+@Target({ElementType.TYPE, ElementType.ANNOTATION_TYPE})
+@Retention(RetentionPolicy.RUNTIME)
+@Inherited
+@Documented
+public @interface TransientAuthentication {
+}