Prepare Token Updates for line#1054 Compatibility

Motivation
To ensure smooth compatibility with line#1054, the `Token` structure needs an update to support changes in `admin` property.

Modifications:
- Enhanced the Token deserializer to accept both `admin` and `systemAdmin` properties, ensuring backward compatibility.
- Updated `MetadataService.updateTokenLevel()` to avoid direct access to the `admin` property.

Result:
- The `Token` structure now supports the upcoming changes, allowing seamless updates with line#1054.

server/src/main/java/com/linecorp/centraldogma/server/metadata/MetadataService.java

@@ -57,6 +57,7 @@
 import com.linecorp.centraldogma.internal.jsonpatch.TestAbsenceOperation;
 import com.linecorp.centraldogma.server.QuotaConfig;
 import com.linecorp.centraldogma.server.command.CommandExecutor;
+import com.linecorp.centraldogma.server.internal.admin.service.TokenNotFoundException;
 import com.linecorp.centraldogma.server.storage.project.Project;
 import com.linecorp.centraldogma.server.storage.project.ProjectManager;
 
@@ -1011,14 +1012,25 @@ public CompletableFuture<Revision> updateTokenLevel(Author author, String appId,
                               "Update the token level: " + appId + " to " + (toBeAdmin ? "admin" : "user"),
                               () -> tokenRepo.fetch(INTERNAL_PROJECT_DOGMA, Project.REPO_DOGMA, TOKEN_JSON)
                                              .thenApply(tokens -> {
-                                                 final JsonPointer adminPath = JsonPointer.compile(
-                                                         "/appIds" + encodeSegment(appId) +
-                                                         "/admin");
+                                                 final Tokens tokens0 = tokens.object();
+                                                 final Token token = tokens0.get(appId);
+                                                 if (token == null) {
+                                                     throw new TokenNotFoundException("App ID: " + appId);
+                                                 }
+                                                 if (toBeAdmin == token.isAdmin()) {
+                                                     throw new IllegalArgumentException(
+                                                             "The token is already " +
+                                                             (toBeAdmin ? "admin" : "user"));
+                                                 }
+                                                 final JsonPointer path = JsonPointer.compile(
+                                                         "/appIds" + encodeSegment(appId));
+
                                                  final Change<JsonNode> change = Change.ofJsonPatch(
                                                          TOKEN_JSON,
-                                                         new ReplaceOperation(adminPath,
-                                                                              Jackson.valueToTree(
-                                                                                      toBeAdmin)).toJsonNode());
+                                                         new ReplaceOperation(
+                                                                 path,
+                                                                 Jackson.valueToTree(token.withAdmin(
+                                                                         toBeAdmin))).toJsonNode());
                                                  return HolderWithRevision.of(change, tokens.revision());
                                              }));
     }

server/src/main/java/com/linecorp/centraldogma/server/metadata/Token.java

@@ -68,7 +68,7 @@ public final class Token implements Identifiable {
     private final UserAndTimestamp deletion;
 
     Token(String appId, String secret, boolean isAdmin, UserAndTimestamp creation) {
-        this(appId, secret, isAdmin, creation, null, null);
+        this(appId, secret, isAdmin, isAdmin, creation, null, null);
     }
 
     /**
@@ -77,13 +77,16 @@ public final class Token implements Identifiable {
     @JsonCreator
     public Token(@JsonProperty("appId") String appId,
                  @JsonProperty("secret") String secret,
-                 @JsonProperty("admin") boolean isAdmin,
+                 // TODO(minwoox): Remove admin field after all tokens are migrated.
+                 @JsonProperty("admin") @Nullable Boolean isAdmin,
+                 @JsonProperty("systemAdmin") @Nullable Boolean isSystemAdmin,
                  @JsonProperty("creation") UserAndTimestamp creation,
                  @JsonProperty("deactivation") @Nullable UserAndTimestamp deactivation,
                  @JsonProperty("deletion") @Nullable UserAndTimestamp deletion) {
+        assert isAdmin != null || isSystemAdmin != null;
         this.appId = Util.validateFileName(appId, "appId");
         this.secret = Util.validateFileName(secret, "secret");
-        this.isAdmin = isAdmin;
+        this.isAdmin = isSystemAdmin != null ? isSystemAdmin : isAdmin;
         this.creation = requireNonNull(creation, "creation");
         this.deactivation = deactivation;
         this.deletion = deletion;
@@ -189,4 +192,17 @@ public String toString() {
     public Token withoutSecret() {
         return new Token(appId(), isAdmin(), creation(), deactivation(), deletion());
     }
+
+    /**
+     * Returns a new {@link Token} instance with {@code isAdmin}.
+     * This method must be called by the token whose secret is not null.
+     */
+    public Token withAdmin(boolean isAdmin) {
+        if (isAdmin == isAdmin()) {
+            return this;
+        }
+        final String secret = secret();
+        assert secret != null;
+        return new Token(appId(), secret, isAdmin, isAdmin, creation(), deactivation(), deletion());
+    }
 }

server/src/test/java/com/linecorp/centraldogma/server/internal/admin/model/SerializationTest.java

@@ -67,7 +67,7 @@ void testValidProject() throws IOException {
         final Member member = new Member(userLogin, ProjectRole.MEMBER, newCreationTag());
         final RepositoryMetadata repositoryMetadata = new RepositoryMetadata("sample", newCreationTag(),
                                                                              PerRolePermissions.ofDefault());
-        final Token token = new Token("testApp", "testSecret", false, newCreationTag(), null, null);
+        final Token token = new Token("testApp", "testSecret", false, false, newCreationTag(), null, null);
         final ProjectMetadata metadata =
                 new ProjectMetadata("test",
                                     ImmutableMap.of(repositoryMetadata.name(), repositoryMetadata),
@@ -141,7 +141,7 @@ void testRemovedProject() throws IOException {
                                          newCreationTag());
         final RepositoryMetadata repositoryMetadata = new RepositoryMetadata("sample", newCreationTag(),
                                                                              PerRolePermissions.ofDefault());
-        final Token token = new Token("testApp", "testSecret", false, newCreationTag(), null, null);
+        final Token token = new Token("testApp", "testSecret", false, false, newCreationTag(), null, null);
         final ProjectMetadata metadata =
                 new ProjectMetadata("test",
                                     ImmutableMap.of(repositoryMetadata.name(), repositoryMetadata),

server/src/test/java/com/linecorp/centraldogma/server/metadata/TokenTest.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2024 LINE Corporation
+ *
+ * LINE Corporation licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package com.linecorp.centraldogma.server.metadata;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+import com.linecorp.centraldogma.internal.Jackson;
+
+class TokenTest {
+
+    private static final String APP_ID = "foo-id";
+    private static final String APP_SECRET = "appToken-foo";
+
+    @Test
+    void deserializeToken() throws Exception {
+        final String legacyTokenJson = tokenJson(true);
+        final Token legacyToken = Jackson.readValue(legacyTokenJson, Token.class);
+        assertThat(legacyToken.appId()).isEqualTo(APP_ID);
+        assertThat(legacyToken.isAdmin()).isTrue();
+
+        final String tokenJson = tokenJson(false);
+        final Token token = Jackson.readValue(tokenJson, Token.class);
+        assertThat(token.appId()).isEqualTo(APP_ID);
+        assertThat(token.isAdmin()).isTrue();
+    }
+
+    private static String tokenJson(boolean legacy) {
+        return "{\"appId\": \"" + APP_ID + "\"," +
+               "  \"secret\": \"" + APP_SECRET + "\"," +
+               (legacy ? "  \"admin\": true," : " \"systemAdmin\": true,") +
+               "  \"creation\": {" +
+               "    \"user\": \"[email protected]\"," +
+               "    \"timestamp\": \"2018-04-10T09:58:20.032Z\"" +
+               "}}";
+    }
+}