Make the loginProcessingUrl configurable for saml2Login()

Fixes gh-7565

https://github.com/spring-projects/spring-security/issues/7565

saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/servlet/filter/Saml2WebSsoAuthenticationFilter.java

@@ -44,9 +44,21 @@ public class Saml2WebSsoAuthenticationFilter extends AbstractAuthenticationProce
 	private final RelyingPartyRegistrationRepository relyingPartyRegistrationRepository;
 
 	public Saml2WebSsoAuthenticationFilter(RelyingPartyRegistrationRepository relyingPartyRegistrationRepository) {
-		super(DEFAULT_FILTER_PROCESSES_URI);
+		this(relyingPartyRegistrationRepository, DEFAULT_FILTER_PROCESSES_URI);
+	}
+
+	public Saml2WebSsoAuthenticationFilter(
+			RelyingPartyRegistrationRepository relyingPartyRegistrationRepository,
+			String filterProcessesUrl) {
+		super(filterProcessesUrl);
 		Assert.notNull(relyingPartyRegistrationRepository, "relyingPartyRegistrationRepository cannot be null");
-		this.matcher = new AntPathRequestMatcher(DEFAULT_FILTER_PROCESSES_URI);
+		Assert.hasText(filterProcessesUrl, "filterProcessesUrl must contain a URL pattern");
+		Assert.isTrue(
+				filterProcessesUrl.contains("{registrationId}"),
+				"filterProcessesUrl must contain a {registrationId} match variable"
+		);
+		this.matcher = new AntPathRequestMatcher(filterProcessesUrl);
+		setRequiresAuthenticationRequestMatcher(this.matcher);
 		this.relyingPartyRegistrationRepository = relyingPartyRegistrationRepository;
 		setAllowSessionCreation(true);
 		setSessionAuthenticationStrategy(new ChangeSessionIdAuthenticationStrategy());

saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/servlet/filter/Saml2WebSsoAuthenticationFilterTests.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2002-2019 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.saml2.provider.service.servlet.filter;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistrationRepository;
+
+import javax.servlet.http.HttpServletResponse;
+
+import static org.mockito.Mockito.mock;
+
+public class Saml2WebSsoAuthenticationFilterTests {
+
+	private Saml2WebSsoAuthenticationFilter filter;
+	private RelyingPartyRegistrationRepository repository = mock(RelyingPartyRegistrationRepository.class);
+	private MockHttpServletRequest request = new MockHttpServletRequest();
+	private HttpServletResponse response = new MockHttpServletResponse();
+
+	@Rule
+	public ExpectedException exception = ExpectedException.none();
+
+	@Before
+	public void setup() {
+		filter = new Saml2WebSsoAuthenticationFilter(repository);
+		request.setPathInfo("/login/saml2/sso/idp-registration-id");
+		request.setParameter("SAMLResponse", "xml-data-goes-here");
+	}
+
+	@Test
+	public void constructingFilterWithMissingRegistrationIdVariableThenThrowsException() {
+		exception.expect(IllegalArgumentException.class);
+		exception.expectMessage("filterProcessesUrl must contain a {registrationId} match variable");
+		filter = new Saml2WebSsoAuthenticationFilter(repository, "/url/missing/variable");
+	}
+
+	@Test
+	public void constructingFilterWithValidRegistrationIdVariableThenSucceeds() {
+		filter = new Saml2WebSsoAuthenticationFilter(repository, "/url/variable/is/present/{registrationId}");
+	}
+
+	@Test
+	public void requiresAuthenticationWhenHappyPathThenReturnsTrue() {
+		Assert.assertTrue(filter.requiresAuthentication(request, response));
+	}
+
+	@Test
+	public void requiresAuthenticationWhenCustomProcessingUrlThenReturnsTrue() {
+		filter = new Saml2WebSsoAuthenticationFilter(repository, "/some/other/path/{registrationId}");
+		request.setPathInfo("/some/other/path/idp-registration-id");
+		request.setParameter("SAMLResponse", "xml-data-goes-here");
+		Assert.assertTrue(filter.requiresAuthentication(request, response));
+	}
+
+
+}