LoginPageGeneratingWebFilter honors context path

Closes gh-8807

web/src/test/java/org/springframework/security/web/server/ui/LoginPageGeneratingWebFilterTests.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2002-2020 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
+ *
+ *      https://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.ui;
+
+import org.junit.Test;
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import reactor.core.publisher.Mono;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+public class LoginPageGeneratingWebFilterTests {
+
+	@Test
+	public void filterWhenLoginWithContextPathThenActionContainsContextPath() throws Exception {
+		LoginPageGeneratingWebFilter filter = new LoginPageGeneratingWebFilter();
+		filter.setFormLoginEnabled(true);
+
+		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/test/login").contextPath("/test"));
+
+		filter.filter(exchange, e -> Mono.empty()).block();
+
+		assertThat(exchange.getResponse().getBodyAsString().block()).contains("action=\"/test/login\"");
+	}
+
+	@Test
+	public void filterWhenLoginWithNoContextPathThenActionDoesNotContainsContextPath() throws Exception {
+		LoginPageGeneratingWebFilter filter = new LoginPageGeneratingWebFilter();
+		filter.setFormLoginEnabled(true);
+
+		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/login"));
+
+		filter.filter(exchange, e -> Mono.empty()).block();
+
+		assertThat(exchange.getResponse().getBodyAsString().block()).contains("action=\"/login\"");
+	}
+}