Improve docs on forwarded headers

Issue: SPR-16660

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/bind/annotation/CrossOrigin.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * 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.
@@ -81,6 +81,13 @@
 	 * <p>A matched origin is listed in the {@code Access-Control-Allow-Origin}
 	 * response header of preflight actual CORS requests.
 	 * <p>By default all origins are allowed.
+	 * <p><strong>Note:</strong> CORS checks use values from "Forwarded"
+	 * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+	 * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+	 * if present, in order to reflect the client-originated address.
+	 * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+	 * central place whether to extract and use, or to discard such headers.
+	 * See the Spring Framework reference for more on this filter.
 	 * @see #value
 	 */
 	@AliasFor("value")

spring-web/src/main/java/org/springframework/web/cors/CorsConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * 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.
@@ -145,6 +145,13 @@ else if (this.allowedOrigins == DEFAULT_PERMIT_ALL) {
 	 * <p>The special value {@code "*"} allows all methods.
 	 * <p>If not set, only {@code "GET"} and {@code "HEAD"} are allowed.
 	 * <p>By default this is not set.
+	 * <p><strong>Note:</strong> CORS checks use values from "Forwarded"
+	 * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+	 * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+	 * if present, in order to reflect the client-originated address.
+	 * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+	 * central place whether to extract and use, or to discard such headers.
+	 * See the Spring Framework reference for more on this filter.
 	 */
 	public void setAllowedMethods(@Nullable List<String> allowedMethods) {
 		this.allowedMethods = (allowedMethods != null ? new ArrayList<>(allowedMethods) : null);

spring-web/src/main/java/org/springframework/web/cors/reactive/CorsUtils.java

@@ -54,6 +54,13 @@ public static boolean isPreFlightRequest(ServerHttpRequest request) {
 	 * @code X-Forwarded-Port} headers.
 	 * @return {@code true} if the request is a same-origin one, {@code false} in case
 	 * of a cross-origin request
+	 * <p><strong>Note:</strong> this method uses values from "Forwarded"
+	 * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+	 * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+	 * if present, in order to reflect the client-originated address.
+	 * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+	 * central place whether to extract and use, or to discard such headers.
+	 * See the Spring Framework reference for more on this filter.
 	 */
 	public static boolean isSameOrigin(ServerHttpRequest request) {
 		String origin = request.getHeaders().getOrigin();

spring-web/src/main/java/org/springframework/web/util/WebUtils.java

@@ -677,6 +677,13 @@ public static MultiValueMap<String, String> parseMatrixVariables(String matrixVa
 	 * Check the given request origin against a list of allowed origins.
 	 * A list containing "*" means that all origins are allowed.
 	 * An empty list means only same origin is allowed.
+	 * <p><strong>Note:</strong> this method may use values from "Forwarded"
+	 * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+	 * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+	 * if present, in order to reflect the client-originated address.
+	 * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+	 * central place whether to extract and use, or to discard such headers.
+	 * See the Spring Framework reference for more on this filter.
 	 * @return {@code true} if the request origin is valid, {@code false} otherwise
 	 * @since 4.1.5
 	 * @see <a href="https://tools.ietf.org/html/rfc6454">RFC 6454: The Web Origin Concept</a>
@@ -701,6 +708,13 @@ else if (CollectionUtils.isEmpty(allowedOrigins)) {
 	 * Check if the request is a same-origin one, based on {@code Origin}, {@code Host},
 	 * {@code Forwarded}, {@code X-Forwarded-Proto}, {@code X-Forwarded-Host} and
 	 * @code X-Forwarded-Port} headers.
+	 * <p><strong>Note:</strong> this method uses values from "Forwarded"
+	 * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+	 * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+	 * if present, in order to reflect the client-originated address.
+	 * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+	 * central place whether to extract and use, or to discard such headers.
+	 * See the Spring Framework reference for more on this filter.
 	 * @return {@code true} if the request is a same-origin one, {@code false} in case
 	 * of cross-origin request
 	 * @since 4.2

spring-webflux/src/main/java/org/springframework/web/reactive/config/CorsRegistration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * 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.
@@ -49,6 +49,13 @@ public CorsRegistration(String pathPattern) {
 	 * <p>A matched origin is listed in the {@code Access-Control-Allow-Origin}
 	 * response header of preflight actual CORS requests.
 	 * <p>By default all origins are allowed.
+	 * <p><strong>Note:</strong> CORS checks use values from "Forwarded"
+	 * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+	 * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+	 * if present, in order to reflect the client-originated address.
+	 * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+	 * central place whether to extract and use, or to discard such headers.
+	 * See the Spring Framework reference for more on this filter.
 	 */
 	public CorsRegistration allowedOrigins(String... origins) {
 		this.config.setAllowedOrigins(new ArrayList<>(Arrays.asList(origins)));

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/CorsRegistration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * 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.
@@ -51,6 +51,13 @@ public CorsRegistration(String pathPattern) {
 	 * <p>A matched origin is listed in the {@code Access-Control-Allow-Origin}
 	 * response header of preflight actual CORS requests.
 	 * <p>By default, all origins are allowed.
+	 * <p><strong>Note:</strong> CORS checks use values from "Forwarded"
+	 * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+	 * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+	 * if present, in order to reflect the client-originated address.
+	 * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+	 * central place whether to extract and use, or to discard such headers.
+	 * See the Spring Framework reference for more on this filter.
 	 */
 	public CorsRegistration allowedOrigins(String... origins) {
 		this.config.setAllowedOrigins(Arrays.asList(origins));

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/MvcUriComponentsBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * 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.
@@ -83,14 +83,13 @@
  * {@link #relativeTo(org.springframework.web.util.UriComponentsBuilder)}.
  * </ul>
  *
- * <p><strong>Note:</strong> This class extracts and uses values from the headers
- * "Forwarded" (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
- * or "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" if
- * "Forwarded" is not found, in order to reflect the client-originated protocol
- * and address. As an alternative consider using the
- * {@link org.springframework.web.filter.ForwardedHeaderFilter} to have such
- * headers extracted once and removed, or removed only (without being used).
- * See the reference for further information including security considerations.
+ * <p><strong>Note:</strong> This class uses values from "Forwarded"
+ * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+ * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+ * if present, in order to reflect the client-originated protocol and address.
+ * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+ * central place whether to extract and use, or to discard such headers.
+ * See the Spring Framework reference for more on this filter.
  *
  * @author Oliver Gierke
  * @author Rossen Stoyanchev

spring-webmvc/src/main/java/org/springframework/web/servlet/support/ServletUriComponentsBuilder.java

@@ -36,14 +36,13 @@
  * UriComponentsBuilder with additional static factory methods to create links
  * based on the current HttpServletRequest.
  *
- * <p><strong>Note:</strong> This class extracts and uses values from the headers
- * "Forwarded" (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
- * or "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" if
- * "Forwarded" is not found, in order to reflect the client-originated protocol
- * and address. As an alternative consider using the
- * {@link org.springframework.web.filter.ForwardedHeaderFilter} to have such
- * headers extracted once and removed, or removed only (without being used).
- * See the reference for further information including security considerations.
+ * <p><strong>Note:</strong> This class uses values from "Forwarded"
+ * (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+ * "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" headers,
+ * if present, in order to reflect the client-originated protocol and address.
+ * Consider using the {@code ForwardedHeaderFilter} in order to choose from a
+ * central place whether to extract and use, or to discard such headers.
+ * See the Spring Framework reference for more on this filter.
  *
  * @author Rossen Stoyanchev
  * @since 3.1

spring-webmvc/src/main/resources/org/springframework/web/servlet/config/spring-mvc.xsd

@@ -1331,6 +1331,12 @@
 								<xsd:documentation><![CDATA[
 	Comma-separated list of origins to allow, e.g. "http://domain1.com, http://domain2.com".
 	The special value "*" allows all domains (default).
+
+	Note that CORS checks use values from "Forwarded" (RFC 7239), "X-Forwarded-Host",
+	"X-Forwarded-Port", and "X-Forwarded-Proto" headers, if present, in order to reflect
+	the client-originated address. Consider using the ForwardedHeaderFilter in order to
+	choose from a central place whether to extract and use such headers, or whether to
+	discard them. See the Spring Framework reference for more on this filter.
 								]]></xsd:documentation>
 							</xsd:annotation>
 						</xsd:attribute>

src/docs/asciidoc/web/webflux.adoc

@@ -854,6 +854,44 @@ views through the <<webflux-config-view-resolvers,WebFlux Config>>. Default view
 always selected and used if they match the requested media type.
 
 
+[[webflux-filters]]
+== Filters
+[.small]#<<web.adoc#filters,Same in Spring MVC>>#
+
+As part of the <<webflux-web-handler-api>>, the `spring-web` module provides a number of
+`WebFilter` implementations.
+
+
+
+[[webflux-filters-forwarded-headers]]
+=== Forwarded Headers
+[.small]#<<web.adoc#filters-forwarded-headers,Same in Spring MVC>>#
+
+As a request goes through proxies such as load balancers the host, port, and
+scheme may change presenting a challenge for applications that need to create links
+to resources since the links should reflect the host, port, and scheme of the
+original request as seen from a client perspective.
+
+https://tools.ietf.org/html/rfc7239[RFC 7239] defines the "Forwarded" HTTP header
+for proxies to use to provide information about the original request. There are also
+other non-standard headers in use such as "X-Forwarded-Host", "X-Forwarded-Port",
+and "X-Forwarded-Proto".
+
+`ForwardedHeaderFilter` detects, extracts, and uses information from the "Forwarded"
+header, or from "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto".
+It wraps the request in order to overlay its host, port, and scheme and also "hides"
+the forwarded headers for subsequent processing.
+
+Note that there are security considerations when using forwarded headers as explained
+in Section 8 of RFC 7239. At the application level it is difficult to determine whether
+forwarded headers can be trusted or not. This is why the network upstream should be
+configured correctly to filter out untrusted forwarded headers from the outside.
+
+Applications that don't have a proxy and don't need to use forwarded headers can
+configure the `ForwardedHeaderFilter` to remove and ignore such headers.
+
+
+
 
 
 [[webflux-controller]]