Support comma-separated X-Forwarded-Proto

Issue: SPR-12816

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

@@ -303,7 +303,8 @@ public class UriComponentsBuilder implements Cloneable {
 
 		String protocolHeader = request.getHeaders().getFirst("X-Forwarded-Proto");
 		if (StringUtils.hasText(protocolHeader)) {
-			scheme = protocolHeader;
+			String[] protocols = StringUtils.commaDelimitedListToStringArray(protocolHeader);
+			scheme = protocols[0];
 		}
 
 		builder.scheme(scheme);

spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java

@@ -417,6 +417,25 @@ public class UriComponentsBuilderTests {
 		assertEquals("http://a.example.org/mvc-showcase", result.toString());
 	}
 
+	// SPR-12816
+
+	@Test
+	public void fromHttpRequestWithForwardedProtoMultiValueHeader() {
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		request.setScheme("http");
+		request.setServerName("localhost");
+		request.setServerPort(8080);
+		request.setRequestURI("/mvc-showcase");
+		request.addHeader("X-Forwarded-Host", "a.example.org");
+		request.addHeader("X-Forwarded-Port", "443");
+		request.addHeader("X-Forwarded-Proto", "https,https");
+
+		HttpRequest httpRequest = new ServletServerHttpRequest(request);
+		UriComponents result = UriComponentsBuilder.fromHttpRequest(httpRequest).build();
+
+		assertEquals("https://a.example.org/mvc-showcase", result.toString());
+	}
+
 	@Test
 	public void path() throws URISyntaxException {
 		UriComponentsBuilder builder = UriComponentsBuilder.fromPath("/foo/bar");