Add authenticated().withAuthentication(Consumer<Authentication>)

This allows arbitrary assertions of the authenticated user

Fixes: gh-4996

test/src/main/java/org/springframework/security/test/web/servlet/response/SecurityMockMvcResultMatchers.java

@@ -17,6 +17,7 @@ package org.springframework.security.test.web.servlet.response;
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.function.Consumer;
 
 import org.springframework.security.authentication.AuthenticationTrustResolver;
 import org.springframework.security.authentication.AuthenticationTrustResolverImpl;
@@ -88,6 +89,7 @@ public final class SecurityMockMvcResultMatchers {
 		private Object expectedAuthenticationPrincipal;
 		private String expectedAuthenticationName;
 		private Collection<? extends GrantedAuthority> expectedGrantedAuthorities;
+		private Consumer<Authentication> assertAuthentication;
 
 		@Override
 		public void match(MvcResult result) throws Exception {
@@ -97,6 +99,10 @@ public final class SecurityMockMvcResultMatchers {
 
 			assertTrue("Authentication should not be null", auth != null);
 
+			if (this.assertAuthentication != null) {
+				this.assertAuthentication.accept(auth);
+			}
+
 			if (this.expectedContext != null) {
 				assertEquals(this.expectedContext + " does not equal " + context,
 						this.expectedContext, context);
@@ -140,6 +146,16 @@ public final class SecurityMockMvcResultMatchers {
 			}
 		}
 
+		/**
+		 * Allows for any validating the authentication with arbitrary assertions
+		 * @param assesrtAuthentication the Consumer which validates the authentication
+		 * @return the AuthenticatedMatcher to perform additional assertions
+		 */
+		public AuthenticatedMatcher withAuthentication(Consumer<Authentication> assesrtAuthentication) {
+			this.assertAuthentication = assesrtAuthentication;
+			return this;
+		}
+
 		/**
 		 * Specifies the expected username
 		 *