Document how to configure access logging

Also, the section on `server.*` configuration was poor so this commit
also improves it.

Closes gh-4989

Author: snicoll

spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -507,6 +507,35 @@ the two to configure programmatically. See the
 {github-code}/spring-boot-samples/spring-boot-sample-tomcat-multi-connectors[`spring-boot-sample-tomcat-multi-connectors`]
 sample project for an example.
 
+[[howto-configure-accesslogs]]
+=== Configure Access Logging
+Access logs can be configured for Tomcat and Undertow via their respective namespaces.
+
+For instance, the following logs access on Tomcat with a
+https://tomcat.apache.org/tomcat-8.0-doc/config/valve.html#Access_Logging[custom pattern].
+
+[source,properties,indent=0,subs="verbatim,quotes,attributes"]
+----
+	server.tomcat.basedir=my-tomcat
+	server.tomcat.accesslog.enabled=true
+	server.tomcat.accesslog.pattern=%t %a "%r" %s (%D ms)
+----
+
+NOTE: The default location for logs is a `logs` directory relative to the tomcat base dir
+and said directory is a temp directory by default so you may want to fix Tomcat's base
+directory or use an absolute path for the logs. In the example above, the logs will
+be available in `my-tomcat/logs` relative to the working directory of the application.
+
+Access logging for undertow can be configured in a similar fashion
+
+[source,properties,indent=0,subs="verbatim,quotes,attributes"]
+----
+	server.undertow.accesslog.enabled=true
+	server.undertow.accesslog.pattern=%t %a "%r" %s (%D ms)
+----
+
+Logs are stored in a `logs` directory relative to the working directory of the
+application. This can be customized via `server.undertow.accesslog.directory`.
 
 
 [[howto-use-behind-a-proxy-server]]

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -1877,11 +1877,22 @@ file.
 
 Common server settings include:
 
-* `server.port` -- The listen port for incoming HTTP requests.
-* `server.address` -- The interface address to bind to.
-* `server.session.timeout` -- A session timeout.
-
-See the {sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[`ServerProperties`]
+* Network settings: listen port for incoming HTTP requests (`server.port`), interface
+address to bind to `server.address`, etc.
+* Session settings: whether the session is persistent (`server.session.persistence`),
+session timeout (`server.session.timeout`), location of session data
+(`server.session.store-dir`) and session-cookie configuration (`server.session.cookie.*`).
+* Error management: location of the error page (`server.error.path`), etc.
+* <<howto.adoc#howto-configure-ssl,SSL>>
+* <<howto.adoc#how-to-enable-http-response-compression,HTTP compression>>
+
+Spring Boot tries as much as possible to expose common settings but this is not always
+possible. For those cases, dedicated namespaces offer server-specific customizations (see
+`server.tomcat` and `server.undertow`). For instance,
+<<howto.adoc#howto-configure-accesslogs,access logs>> can be configured with specific
+features of the embedded servlet container.
+
+TIP: See the {sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[`ServerProperties`]
 class for a complete list.