SEC-2868: Simplify custom UserDetailsService Java Config

Exposing a UserDetailsService as a bean is now all that is necessary
for Java based configuration. Additionally, an optional PasswordEncoder
bean can be used to configure password encoding.

docs/manual/src/docs/asciidoc/index.adoc

@@ -374,6 +374,7 @@ This will give you access to the entire project history (including all releases
 ** <<method-security-meta-annotations,Method Security Meta Annotations>>
 * <<el-access-web-path-variables,Path Variables in Web Security Expressions>>
 * <<test-method-withanonymoususer,@WithAnonymousUser>>
+* <<jc-authentication-userdetailsservice,Simplified UserDetailsService Java Configuration>>
 
 === What's new in Spring Security 4.0
 
@@ -912,6 +913,33 @@ cn: admin
 uniqueMember: uid=admin,ou=people,dc=springframework,dc=org
 ----
 
+[[jc-authentication-userdetailsservice]]
+==== UserDetailsService
+
+You can define custom authentication by exposing a custom `UserDetailsService` as a bean.
+For example, the following will customize authentication assuming that `SpringDataUserDetailsService` implements `UserDetailsService`:
+
+[source,java]
+----
+@Bean
+public SpringDataUserDetailsService springDataUserDetailsService() {
+    return new SpringDataUserDetailsService();
+}
+----
+
+You can also customize how passwords are encoded by exposing a `PasswordEncoder` as a bean.
+For example, if you use bcrypt you can add a bean definition as shown below:
+
+[source,java]
+----
+@Bean
+public BCryptPasswordEncoder passwordEncoder() {
+    return new BCryptPasswordEncoder();
+}
+----
+
+==== LDAP Authentication
+
 === Multiple HttpSecurity
 
 We can configure multiple HttpSecurity instances just as we can have multiple `<http>` blocks. The key is to extend the `WebSecurityConfigurationAdapter` multiple times. For example, the following is an example of having a different configuration for URL's that start with `/api/`.