Add ForwardedHeaderFilter requestOnly

Add an option for ForwardedHeaderFilter to only process the
HttpServletRequest. This means that HttpServletResponse.sendRedirect will
only work when the application is conifgured to use relative redirects
using Servlet Container specific setup.

Issue: SPR-15717

spring-web/src/main/java/org/springframework/web/filter/ForwardedHeaderFilter.java

@@ -79,6 +79,8 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 
 	private boolean removeOnly;
 
+	private boolean requestOnly;
+
 
 	public ForwardedHeaderFilter() {
 		this.pathHelper = new UrlPathHelper();
@@ -97,6 +99,20 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 		this.removeOnly = removeOnly;
 	}
 
+	/**
+	 * Enables mode in which only the HttpServletRequest is modified. This means that
+	 * {@link HttpServletResponse#sendRedirect(String)} will only work when the application is configured to use
+	 * relative redirects. This can be done with Servlet Container specific setup. For example,  using Tomcat's
+	 * <a href="https://tomcat.apache.org/tomcat-8.0-doc/config/context.html#Common_Attributes">useRelativeRedirects</a>
+	 * attribute.
+	 *
+	 * @param requestOnly whether to customize the {@code HttpServletResponse} or not. Default is false (customize the
+	 * {@code HttpServletResponse})
+	 * @since 4.3.10
+	 */
+	public void setRequestOnly(boolean requestOnly) {
+		this.requestOnly = requestOnly;
+	}
 
 	@Override
 	protected boolean shouldNotFilter(HttpServletRequest request) throws ServletException {
@@ -130,7 +146,8 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 		}
 		else {
 			HttpServletRequest theRequest = new ForwardedHeaderExtractingRequest(request, this.pathHelper);
-			HttpServletResponse theResponse = new ForwardedHeaderExtractingResponse(response, theRequest);
+			HttpServletResponse theResponse = this.requestOnly ? response :
+					new ForwardedHeaderExtractingResponse(response, theRequest);
 			filterChain.doFilter(theRequest, theResponse);
 		}
 	}

spring-web/src/test/java/org/springframework/web/filter/ForwardedHeaderFilterTests.java

@@ -403,6 +403,26 @@ public class ForwardedHeaderFilterTests {
 		assertEquals("../foo/bar", redirectedUrl);
 	}
 
+	@Test
+	public void sendRedirectWhenRequestOnlyAndXForwardedThenUsesRelativeRedirects() throws Exception {
+		this.request.addHeader(X_FORWARDED_PROTO, "https");
+		this.request.addHeader(X_FORWARDED_HOST, "example.com");
+		this.request.addHeader(X_FORWARDED_PORT, "443");
+		this.filter.setRequestOnly(true);
+
+		String location = sendRedirect("/a");
+
+		assertEquals("/a", location);
+	}
+
+	@Test
+	public void sendRedirectWhenRequestOnlyAndNoXForwardedThenUsesRelativeRedirects() throws Exception {
+		this.filter.setRequestOnly(true);
+
+		String location = sendRedirect("/a");
+
+		assertEquals("/a", location);
+	}
 
 	private String sendRedirect(final String location) throws ServletException, IOException {
 		MockHttpServletResponse response = doWithFiltersAndGetResponse(this.filter, new OncePerRequestFilter() {