anchor.diff:  
   .Access Currently Authenticated User
   ====
  -[source,java]
  +.Java
  +[source,java,role="primary"]
   ----
   SecurityContext context = SecurityContextHolder.getContext();
   Authentication authentication = context.getAuthentication();
   String username = authentication.getName();
   Object principal = authentication.getPrincipal();
   Collection<? extends GrantedAuthority> authorities = authentication.getAuthorities();
  +----
  +
  +.Kotlin
  +[source,kotlin,role="secondary"]
  +----
  +val context = SecurityContextHolder.getContext()
  +val authentication = context.authentication
  +val username = authentication.name
  +val principal = authentication.principal
  +val authorities = authentication.authorities
   ----
   ====
   
  
positive.code: 
  .Setting `SecurityContextHolder`
  ====
  [source,java]
  ----
  SecurityContext context = SecurityContextHolder.createEmptyContext(); // <1>
  Authentication authentication =
  
negative.code: context.setAuthentication(authentication);
  
  SecurityContextHolder.setContext(context); // <3>
  ----
  
  .Kotlin
  [source,kotlin,role="secondary"]
  ----
  val context: SecurityContext = SecurityContextHolder.createEmptyContext() // <1>
  val authentication: Authentication = TestingAuthenticationToken("username", "password", "ROLE_USER") // <2>
  context.authentication = authentication
  
  SecurityContextHolder.setContext(context) // <3>
  ----
  ====
  
  