Add HttpStatusServerEntryPoint

An HttpStatusServerEntryPoint is missing on the
reactive side - essentially the reactive equivalent of
HttpStatusEntryPoint.

Fixes gh-5082

web/src/main/java/org/springframework/security/web/server/authentication/HttpStatusServerEntryPoint.java

@@ -0,0 +1,47 @@
+/*
+ * 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.web.server.authentication;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.security.core.AuthenticationException;
+import org.springframework.security.web.server.ServerAuthenticationEntryPoint;
+import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebExchange;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * A {@link ServerAuthenticationEntryPoint} that sends a generic {@link HttpStatus} as a
+ * response. Useful for JavaScript clients which cannot use Basic authentication since the
+ * browser intercepts the response.
+ *
+ * @author Eric Deandrea
+ * @since 5.1
+ */
+public class HttpStatusServerEntryPoint implements ServerAuthenticationEntryPoint {
+	private final HttpStatus httpStatus;
+
+	public HttpStatusServerEntryPoint(HttpStatus httpStatus) {
+		Assert.notNull(httpStatus, "httpStatus cannot be null");
+		this.httpStatus = httpStatus;
+	}
+
+	@Override
+	public Mono<Void> commence(ServerWebExchange exchange, AuthenticationException authException) {
+		return Mono.fromRunnable(() -> exchange.getResponse().setStatusCode(this.httpStatus));
+	}
+}