Convert 'KnownUsers' to Java (#3799)

pom.xml

@@ -224,6 +224,11 @@
             <artifactId>slf4j-simple</artifactId>
             <version>2.0.12</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>2.10.1</version>
+        </dependency>
 
     </dependencies>
 

src/main/java/io/jenkins/infra/repository_permissions_updater/KnownUsers.java

@@ -0,0 +1,43 @@
+package io.jenkins.infra.repository_permissions_updater;
+
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.util.Set;
+import java.util.TreeSet;
+import com.google.gson.Gson;
+import com.google.gson.reflect.TypeToken;
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+
+public class KnownUsers {
+    private static final String ARTIFACTORY_USER_NAMES_URL = System.getProperty("artifactoryUserNamesJsonListUrl", "https://reports.jenkins.io/artifactory-ldap-users-report.json");
+    private static final String JIRA_USER_NAMES_URL = System.getProperty("jiraUserNamesJsonListUrl", "https://reports.jenkins.io/jira-users-report.json");
+
+    private static Set<String> knownArtifactoryUsers = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
+    private static Set<String> knownJiraUsers = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
+
+    static {
+        try {
+            knownArtifactoryUsers.addAll(parseJson(new URL(ARTIFACTORY_USER_NAMES_URL)));
+            knownJiraUsers.addAll(parseJson(new URL(JIRA_USER_NAMES_URL)));
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    @SuppressFBWarnings(value = "URLCONNECTION_SSRF_FD", justification = "Not relevant in this situation.")
+    private static Set<String> parseJson(URL url) throws IOException {
+        try (InputStreamReader reader = new InputStreamReader(url.openStream(), StandardCharsets.UTF_8)) {
+            return new Gson().fromJson(reader, new TypeToken<Set<String>>(){}.getType());
+        }
+    }
+
+    public static boolean existsInArtifactory(String username) {
+        return knownArtifactoryUsers.contains(username);
+    }
+
+    public static boolean existsInJira(String username) {
+        return knownJiraUsers.contains(username);
+    }
+}