Update RemoteIpValve’s default internal proxies to include 172.16/12

Closes gh-2699

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -294,7 +294,10 @@ public class ServerProperties implements EmbeddedServletContainerCustomizer, Ord
 		private String internalProxies = "10\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}|" // 10/8
 				+ "192\\.168\\.\\d{1,3}\\.\\d{1,3}|" // 192.168/16
 				+ "169\\.254\\.\\d{1,3}\\.\\d{1,3}|" // 169.254/16
-				+ "127\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}"; // 127/8
+				+ "127\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}|" // 127/8
+				+ "172\\.1[6-9]{1}\\.\\d{1,3}\\.\\d{1,3}|" // 172.16/12
+				+ "172\\.2[0-9]{1}\\.\\d{1,3}\\.\\d{1,3}|"
+				+ "172\\.3[0-1]{1}\\.\\d{1,3}\\.\\d{1,3}";
 
 		/**
 		 * Header that holds the incoming protocol, usually named "X-Forwarded-Proto".

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -83,7 +83,10 @@ content into your application; rather pick only the properties that you need.
 	server.tomcat.internal-proxies=10\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}|\\
 			192\\.168\\.\\d{1,3}\\.\\d{1,3}|\\
 			169\\.254\\.\\d{1,3}\\.\\d{1,3}|\\
-			127\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3} # regular expression matching trusted IP addresses
+			127\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}|\\
+			172\\.1[6-9]{1}\\.\\d{1,3}\\.\\d{1,3}|\\
+			172\\.2[0-9]{1}\\.\\d{1,3}\\.\\d{1,3}|\\
+			172\\.3[0-1]{1}\\.\\d{1,3}\\.\\d{1,3} # regular expression matching trusted IP addresses
 	server.tomcat.protocol-header=x-forwarded-proto # front end proxy forward header
 	server.tomcat.port-header= # front end proxy port header
 	server.tomcat.remote-ip-header=x-forwarded-for