Closes #793 Allow API access to Elide for services without user authentication

Author: bukajsytlos

src/main/java/com/faforever/api/security/AuditService.java

@@ -17,18 +17,14 @@ public AuditService(UserSupplier userSupplier) {
 
   public void logMessage(String message) {
     final String extendedMessage = userSupplier.get()
-      .map(fafAuthenticationToken -> {
-        //move to switch pattern matching with java 21
-        if (fafAuthenticationToken instanceof FafUserAuthenticationToken fafUserAuthenticationToken) {
-          return MessageFormat.format("{0} [invoked by User ''{1}'' with id ''{2}'']",
+      .map(fafAuthenticationToken ->
+        switch (fafAuthenticationToken) {
+          case FafUserAuthenticationToken fafUserAuthenticationToken -> MessageFormat.format("{0} [invoked by User ''{1}'' with id ''{2}'']",
             message, fafUserAuthenticationToken.getUsername(), fafUserAuthenticationToken.getUserId());
-        } else if (fafAuthenticationToken instanceof FafServiceAuthenticationToken fafServiceAuthenticationToken) {
-          return MessageFormat.format("{0} [invoked by Service ''{1}'']",
+          case FafServiceAuthenticationToken fafServiceAuthenticationToken -> MessageFormat.format("{0} [invoked by Service ''{1}'']",
             message, fafServiceAuthenticationToken.getServiceName());
-        } else {
-          throw new RuntimeException();
         }
-      })
+      )
       .orElseGet(() -> MessageFormat.format("{0} [invoked by Annonymous user]", message));
     log.info(extendedMessage);
   }

src/main/java/com/faforever/api/security/FafAuthenticationConverter.java

@@ -6,6 +6,7 @@
 
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 
 /**
  * Jwt converter that reads scopes + custom FAF roles from the token extension.
@@ -18,24 +19,18 @@ public AbstractAuthenticationToken convert(Jwt source) {
     List<FafRole> roles = extractRoles(source);
 
     String subject = extractSubject(source);
-
-    try {
-      int userId = Integer.parseInt(subject);
-      String username = extractUsername(source);
-      return new FafUserAuthenticationToken(userId, username, scopes, roles);
-    } catch (NumberFormatException e) {
-      return new FafServiceAuthenticationToken(subject, scopes);
-    }
+    return extractUsername(source)
+      .<FafAuthenticationToken>map(username -> new FafUserAuthenticationToken(Integer.parseInt(subject), username, scopes, roles))
+      .orElseGet(() -> new FafServiceAuthenticationToken(subject, scopes));
   }
 
   private String extractSubject(Jwt source) {
     return source.getSubject();
   }
 
-  private String extractUsername(Jwt source) {
+  private Optional<String> extractUsername(Jwt source) {
     Map<String, Object> ext = source.getClaim("ext");
-    String username = (String) ext.getOrDefault("username", "[undefined]");
-    return username;
+    return Optional.ofNullable((String) ext.get("username"));
   }
 
   private List<FafScope> extractScopes(Jwt source) {