feat: account migration (#10507)

* add Move activity

* add endpoint to move from local to remote

* follow move activity coming to inbox

* fix move endpoint

* add known-as endpoint to create account alias

* add migration page

* add route to migration page

* add move and known-as endpoints

* fix dependnecies error

* fix new endpoints

* fix move activity id

* fix refollow

* add movedToUri and alsoKnownAs to api

* fix moveToUri indicator

* fix missing context

* add chengelog

* rename MkMoved to MkAccountMoved

* add missing semicolon

* fix targetUri

* fix followings query

* remove redundant null check

14 files changed, 534 insertions, 55 deletions

diff --git a/packages/backend/src/core/AccountMoveService.ts b/packages/backend/src/core/AccountMoveService.ts
new file mode 100644
index 0000000000..6a7727c57a
--- /dev/null
+++ b/packages/backend/src/core/AccountMoveService.ts
@@ -0,0 +1,114 @@
+import { Inject, Injectable } from '@nestjs/common';
+import { IsNull } from 'typeorm';
+
+import { bindThis } from '@/decorators.js';
+import { DI } from '@/di-symbols.js';
+import type { LocalUser } from '@/models/entities/User.js';
+import { User } from '@/models/entities/User.js';
+import type { FollowingsRepository, UsersRepository } from '@/models/index.js';
+
+import { GlobalEventService } from '@/core/GlobalEventService.js';
+import { UserFollowingService } from '@/core/UserFollowingService.js';
+import { ApDeliverManagerService } from '@/core/activitypub/ApDeliverManagerService.js';
+import { ApRendererService } from '@/core/activitypub/ApRendererService.js';
+import { UserEntityService } from '@/core/entities/UserEntityService.js';
+import { AccountUpdateService } from '@/core/AccountUpdateService.js';
+import { RelayService } from '@/core/RelayService.js';
+
+@Injectable()
+export class AccountMoveService {
+	constructor(
+		@Inject(DI.usersRepository)
+		private usersRepository: UsersRepository,
+
+		@Inject(DI.followingsRepository)
+		private followingsRepository: FollowingsRepository,
+
+		private userEntityService: UserEntityService,
+		private apRendererService: ApRendererService,
+		private apDeliverManagerService: ApDeliverManagerService,
+		private globalEventService: GlobalEventService,
+		private userFollowingService: UserFollowingService,
+		private accountUpdateService: AccountUpdateService,
+		private relayService: RelayService,
+	) {
+	}
+
+	/**
+	 * Move a local account to a remote account.
+	 *
+	 * After delivering Move activity, its local followers unfollow the old account and then follow the new one.
+	 */
+	@bindThis
+	public async moveToRemote(src: LocalUser, dst: User): Promise<unknown> {
+		// Make sure that the destination is a remote account.
+		if (this.userEntityService.isLocalUser(dst)) throw new Error('move destiantion is not remote');
+		if (!dst.uri) throw new Error('destination uri is empty');
+
+		// add movedToUri to indicate that the user has moved
+		const update = {} as Partial<User>;
+		update.alsoKnownAs = src.alsoKnownAs?.concat([dst.uri]) ?? [dst.uri];
+		update.movedToUri = dst.uri;
+		await this.usersRepository.update(src.id, update);
+
+		const srcPerson = await this.apRendererService.renderPerson(src);
+		const updateAct = this.apRendererService.addContext(this.apRendererService.renderUpdate(srcPerson, src));
+		await this.apDeliverManagerService.deliverToFollowers(src, updateAct);
+		this.relayService.deliverToRelays(src, updateAct);
+
+		// Deliver Move activity to the followers of the old account
+		const moveAct = this.apRendererService.addContext(this.apRendererService.renderMove(src, dst));
+		await this.apDeliverManagerService.deliverToFollowers(src, moveAct);
+
+		// Publish meUpdated event
+		const iObj = await this.userEntityService.pack<true, true>(src.id, src, { detail: true, includeSecrets: true });
+		this.globalEventService.publishMainStream(src.id, 'meUpdated', iObj);
+
+		// follow the new account and unfollow the old one
+		const followings = await this.followingsRepository.find({
+			relations: {
+				follower: true,
+			},
+			where: {
+				followeeId: src.id,
+				followerHost: IsNull(), // follower is local
+			}
+		});
+		followings.forEach(async (following) => {
+			if (!following.follower) return;
+			try {
+				await this.userFollowingService.follow(following.follower, dst);
+				await this.userFollowingService.unfollow(following.follower, src);
+			} catch {
+				/* empty */
+			}
+		});
+
+		return iObj;
+	}
+
+	/**
+	 * Create an alias of an old remote account.
+	 *
+	 * The user's new profile will be published to the followers.
+	 */
+	@bindThis
+	public async createAlias(me: LocalUser, updates: Partial<User>): Promise<unknown> {
+		await this.usersRepository.update(me.id, updates);
+
+		// Publish meUpdated event
+		const iObj = await this.userEntityService.pack<true, true>(me.id, me, {
+			detail: true,
+			includeSecrets: true,
+		});
+		this.globalEventService.publishMainStream(me.id, 'meUpdated', iObj);
+
+		if (me.isLocked === false) {
+			await this.userFollowingService.acceptAllFollowRequests(me);
+		}
+
+		this.accountUpdateService.publishToFollowers(me.id);
+
+		return iObj;
+	}
+}
diff --git a/packages/backend/src/core/AccountUpdateService.ts b/packages/backend/src/core/AccountUpdateService.ts
index d8ba7b169d..b146fc66be 100644
--- a/packages/backend/src/core/AccountUpdateService.ts
+++ b/packages/backend/src/core/AccountUpdateService.ts
@@ -29,7 +29,7 @@ export class AccountUpdateService {
 	public async publishToFollowers(userId: User['id']) {
 		const user = await this.usersRepository.findOneBy({ id: userId });
 		if (user == null) throw new Error('user not found');
-	
+
 		// フォロワーがリモートユーザーかつ投稿者がローカルユーザーならUpdateを配信
 		if (this.userEntityService.isLocalUser(user)) {
 			const content = this.apRendererService.addContext(this.apRendererService.renderUpdate(await this.apRendererService.renderPerson(user), user));
diff --git a/packages/backend/src/core/CoreModule.ts b/packages/backend/src/core/CoreModule.ts
index ea6e229610..8775536e4a 100644
--- a/packages/backend/src/core/CoreModule.ts
+++ b/packages/backend/src/core/CoreModule.ts
@@ -1,4 +1,5 @@
 import { Module } from '@nestjs/common';
+import { AccountMoveService } from './AccountMoveService.js';
 import { AccountUpdateService } from './AccountUpdateService.js';
 import { AiService } from './AiService.js';
 import { AntennaService } from './AntennaService.js';
@@ -119,6 +120,7 @@ import type { Provider } from '@nestjs/common';
 
 //#region 文字列ベースでのinjection用(循環参照対応のため)
 const $LoggerService: Provider = { provide: 'LoggerService', useExisting: LoggerService };
+const $AccountMoveService: Provider = { provide: 'AccountMoveService', useExisting: AccountMoveService };
 const $AccountUpdateService: Provider = { provide: 'AccountUpdateService', useExisting: AccountUpdateService };
 const $AiService: Provider = { provide: 'AiService', useExisting: AiService };
 const $AntennaService: Provider = { provide: 'AntennaService', useExisting: AntennaService };
@@ -242,6 +244,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 	],
 	providers: [
 		LoggerService,
+		AccountMoveService,
 		AccountUpdateService,
 		AiService,
 		AntennaService,
@@ -359,6 +362,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 
 		//#region 文字列ベースでのinjection用(循環参照対応のため)
 		$LoggerService,
+		$AccountMoveService,
 		$AccountUpdateService,
 		$AiService,
 		$AntennaService,
@@ -477,6 +481,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 	exports: [
 		QueueModule,
 		LoggerService,
+		AccountMoveService,
 		AccountUpdateService,
 		AiService,
 		AntennaService,
@@ -593,6 +598,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 
 		//#region 文字列ベースでのinjection用(循環参照対応のため)
 		$LoggerService,
+		$AccountMoveService,
 		$AccountUpdateService,
 		$AiService,
 		$AntennaService,
diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index 055bffe731..40d7ba551d 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -1,5 +1,5 @@
 import { Inject, Injectable } from '@nestjs/common';
-import { In } from 'typeorm';
+import { In, IsNull } from 'typeorm';
 import { DI } from '@/di-symbols.js';
 import type { Config } from '@/config.js';
 import { UserFollowingService } from '@/core/UserFollowingService.js';
@@ -22,7 +22,7 @@ import { QueueService } from '@/core/QueueService.js';
 import type { UsersRepository, NotesRepository, FollowingsRepository, AbuseUserReportsRepository, FollowRequestsRepository } from '@/models/index.js';
 import { bindThis } from '@/decorators.js';
 import type { RemoteUser } from '@/models/entities/User.js';
-import { getApId, getApIds, getApType, isAccept, isActor, isAdd, isAnnounce, isBlock, isCollection, isCollectionOrOrderedCollection, isCreate, isDelete, isFlag, isFollow, isLike, isPost, isReject, isRemove, isTombstone, isUndo, isUpdate, validActor, validPost } from './type.js';
+import { getApHrefNullable, getApId, getApIds, getApType, getOneApHrefNullable, isAccept, isActor, isAdd, isAnnounce, isBlock, isCollection, isCollectionOrOrderedCollection, isCreate, isDelete, isFlag, isFollow, isLike, isMove, isPost, isReject, isRemove, isTombstone, isUndo, isUpdate, validActor, validPost } from './type.js';
 import { ApNoteService } from './models/ApNoteService.js';
 import { ApLoggerService } from './ApLoggerService.js';
 import { ApDbResolverService } from './ApDbResolverService.js';
@@ -31,7 +31,7 @@ import { ApAudienceService } from './ApAudienceService.js';
 import { ApPersonService } from './models/ApPersonService.js';
 import { ApQuestionService } from './models/ApQuestionService.js';
 import type { Resolver } from './ApResolverService.js';
-import type { IAccept, IAdd, IAnnounce, IBlock, ICreate, IDelete, IFlag, IFollow, ILike, IObject, IReject, IRemove, IUndo, IUpdate } from './type.js';
+import type { IAccept, IAdd, IAnnounce, IBlock, ICreate, IDelete, IFlag, IFollow, ILike, IObject, IReject, IRemove, IUndo, IUpdate, IMove } from './type.js';
 
 @Injectable()
 export class ApInboxService {
@@ -80,7 +80,7 @@ export class ApInboxService {
 	) {
 		this.logger = this.apLoggerService.logger;
 	}
-	
+
 	@bindThis
 	public async performActivity(actor: RemoteUser, activity: IObject) {
 		if (isCollectionOrOrderedCollection(activity)) {
@@ -139,6 +139,8 @@ export class ApInboxService {
 			await this.block(actor, activity);
 		} else if (isFlag(activity)) {
 			await this.flag(actor, activity);
+		} else if (isMove(activity)) {
+			await this.move(actor, activity);
 		} else {
 			this.logger.warn(`unrecognized activity type: ${activity.type}`);
 		}
@@ -147,15 +149,15 @@ export class ApInboxService {
 	@bindThis
 	private async follow(actor: RemoteUser, activity: IFollow): Promise<string> {
 		const followee = await this.apDbResolverService.getUserFromApId(activity.object);
-	
+
 		if (followee == null) {
 			return 'skip: followee not found';
 		}
-	
+
 		if (followee.host != null) {
 			return 'skip: フォローしようとしているユーザーはローカルユーザーではありません';
 		}
-	
+
 		await this.userFollowingService.follow(actor, followee, activity.id);
 		return 'ok';
 	}
@@ -183,16 +185,16 @@ export class ApInboxService {
 		const uri = activity.id ?? activity;
 
 		this.logger.info(`Accept: ${uri}`);
-	
+
 		const resolver = this.apResolverService.createResolver();
-	
+
 		const object = await resolver.resolve(activity.object).catch(err => {
 			this.logger.error(`Resolution failed: ${err}`);
 			throw err;
 		});
-	
+
 		if (isFollow(object)) return await this.acceptFollow(actor, object);
-	
+
 		return `skip: Unknown Accept type: ${getApType(object)}`;
 	}
 
@@ -225,18 +227,18 @@ export class ApInboxService {
 		if ('actor' in activity && actor.uri !== activity.actor) {
 			throw new Error('invalid actor');
 		}
-	
+
 		if (activity.target == null) {
 			throw new Error('target is null');
 		}
-	
+
 		if (activity.target === actor.featured) {
 			const note = await this.apNoteService.resolveNote(activity.object);
 			if (note == null) throw new Error('note not found');
 			await this.notePiningService.addPinned(actor, note.id);
 			return;
 		}
-	
+
 		throw new Error(`unknown target: ${activity.target}`);
 	}
 
@@ -405,10 +407,10 @@ export class ApInboxService {
 		if ('actor' in activity && actor.uri !== activity.actor) {
 			throw new Error('invalid actor');
 		}
-	
+
 		// 削除対象objectのtype
 		let formerType: string | undefined;
-	
+
 		if (typeof activity.object === 'string') {
 			// typeが不明だけど、どうせ消えてるのでremote resolveしない
 			formerType = undefined;
@@ -420,19 +422,19 @@ export class ApInboxService {
 				formerType = toSingle(object.type);
 			}
 		}
-	
+
 		const uri = getApId(activity.object);
-	
+
 		// type不明でもactorとobjectが同じならばそれはPersonに違いない
 		if (!formerType && actor.uri === uri) {
 			formerType = 'Person';
 		}
-	
+
 		// それでもなかったらおそらくNote
 		if (!formerType) {
 			formerType = 'Note';
 		}
-	
+
 		if (validPost.includes(formerType)) {
 			return await this.deleteNote(actor, uri);
 		} else if (validActor.includes(formerType)) {
@@ -445,44 +447,44 @@ export class ApInboxService {
 	@bindThis
 	private async deleteActor(actor: RemoteUser, uri: string): Promise<string> {
 		this.logger.info(`Deleting the Actor: ${uri}`);
-	
+
 		if (actor.uri !== uri) {
 			return `skip: delete actor ${actor.uri} !== ${uri}`;
 		}
-	
+
 		const user = await this.usersRepository.findOneBy({ id: actor.id });
 		if (user == null) {
 			return 'skip: actor not found';
 		} else if (user.isDeleted) {
 			return 'skip: already deleted';
 		}
-	
+
 		const job = await this.queueService.createDeleteAccountJob(actor);
-	
+
 		await this.usersRepository.update(actor.id, {
 			isDeleted: true,
 		});
-	
+
 		return `ok: queued ${job.name} ${job.id}`;
 	}
 
 	@bindThis
 	private async deleteNote(actor: RemoteUser, uri: string): Promise<string> {
 		this.logger.info(`Deleting the Note: ${uri}`);
-	
+
 		const unlock = await this.appLockService.getApLock(uri);
-	
+
 		try {
 			const note = await this.apDbResolverService.getNoteFromApId(uri);
-	
+
 			if (note == null) {
 				return 'message not found';
 			}
-	
+
 			if (note.userId !== actor.id) {
 				return '投稿を削除しようとしているユーザーは投稿の作成者ではありません';
 			}
-	
+
 			await this.noteDeleteService.delete(actor, note);
 			return 'ok: note deleted';
 		} finally {
@@ -536,23 +538,23 @@ export class ApInboxService {
 	@bindThis
 	private async rejectFollow(actor: RemoteUser, activity: IFollow): Promise<string> {
 		// ※ activityはこっちから投げたフォローリクエストなので、activity.actorは存在するローカルユーザーである必要がある
-	
+
 		const follower = await this.apDbResolverService.getUserFromApId(activity.actor);
-	
+
 		if (follower == null) {
 			return 'skip: follower not found';
 		}
-	
+
 		if (!this.userEntityService.isLocalUser(follower)) {
 			return 'skip: follower is not a local user';
 		}
-	
+
 		// relay
 		const match = activity.id?.match(/follow-relay\/(\w+)/);
 		if (match) {
 			return await this.relayService.relayRejected(match[1]);
 		}
-	
+
 		await this.userFollowingService.remoteReject(actor, follower);
 		return 'ok';
 	}
@@ -562,18 +564,18 @@ export class ApInboxService {
 		if ('actor' in activity && actor.uri !== activity.actor) {
 			throw new Error('invalid actor');
 		}
-	
+
 		if (activity.target == null) {
 			throw new Error('target is null');
 		}
-	
+
 		if (activity.target === actor.featured) {
 			const note = await this.apNoteService.resolveNote(activity.object);
 			if (note == null) throw new Error('note not found');
 			await this.notePiningService.removePinned(actor, note.id);
 			return;
 		}
-	
+
 		throw new Error(`unknown target: ${activity.target}`);
 	}
 
@@ -582,24 +584,24 @@ export class ApInboxService {
 		if ('actor' in activity && actor.uri !== activity.actor) {
 			throw new Error('invalid actor');
 		}
-	
+
 		const uri = activity.id ?? activity;
-	
+
 		this.logger.info(`Undo: ${uri}`);
-	
+
 		const resolver = this.apResolverService.createResolver();
-	
+
 		const object = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
 			throw e;
 		});
-	
+
 		if (isFollow(object)) return await this.undoFollow(actor, object);
 		if (isBlock(object)) return await this.undoBlock(actor, object);
 		if (isLike(object)) return await this.undoLike(actor, object);
 		if (isAnnounce(object)) return await this.undoAnnounce(actor, object);
 		if (isAccept(object)) return await this.undoAccept(actor, object);
-	
+
 		return `skip: unknown object type ${getApType(object)}`;
 	}
 
@@ -609,17 +611,17 @@ export class ApInboxService {
 		if (follower == null) {
 			return 'skip: follower not found';
 		}
-	
+
 		const following = await this.followingsRepository.findOneBy({
 			followerId: follower.id,
 			followeeId: actor.id,
 		});
-	
+
 		if (following) {
 			await this.userFollowingService.unfollow(follower, actor);
 			return 'ok: unfollowed';
 		}
-	
+
 		return 'skip: フォローされていない';
 	}
 
@@ -708,16 +710,16 @@ export class ApInboxService {
 		if ('actor' in activity && actor.uri !== activity.actor) {
 			return 'skip: invalid actor';
 		}
-	
+
 		this.logger.debug('Update');
-	
+
 		const resolver = this.apResolverService.createResolver();
-	
+
 		const object = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
 			throw e;
 		});
-	
+
 		if (isActor(object)) {
 			await this.apPersonService.updatePerson(actor.uri!, resolver, object);
 			return 'ok: Person updated';
@@ -728,4 +730,55 @@ export class ApInboxService {
 			return `skip: Unknown type: ${getApType(object)}`;
 		}
 	}
+
+	@bindThis
+	private async move(actor: RemoteUser, activity: IMove): Promise<string> {
+		// fetch the new and old accounts
+		const targetUri = getApHrefNullable(activity.target);
+		if (!targetUri) return 'skip: invalid activity target';
+		const new_acc = await this.apPersonService.resolvePerson(targetUri);
+		const old_acc = await this.apPersonService.resolvePerson(actor.uri);
+
+		// update them if they're remote
+		if (new_acc.uri) await this.apPersonService.updatePerson(new_acc.uri);
+		if (old_acc.uri) await this.apPersonService.updatePerson(old_acc.uri);
+
+		// check if alsoKnownAs of the new account is valid
+		let isValidMove = true;
+		if (old_acc.uri) {
+			if (!new_acc.alsoKnownAs?.includes(old_acc.uri)) {
+				isValidMove = false;
+			}
+		} else if (!new_acc.alsoKnownAs?.includes(old_acc.id)) {
+			isValidMove = false;
+		}
+		if (!isValidMove) {
+			return 'skip: accounts invalid';
+		}
+
+		// add target uri to movedToUri in order to indicate that the user has moved
+		await this.usersRepository.update(old_acc.id, { movedToUri: targetUri });
+
+		// follow the new account and unfollow the old one
+		const followings = await this.followingsRepository.find({
+			relations: {
+				follower: true,
+			},
+			where: {
+				followeeId: old_acc.id,
+				followerHost: IsNull(), // follower is local
+			}
+		});
+		followings.forEach(async (following) => {
+			if (!following.follower) return;
+			try {
+				await this.userFollowingService.follow(following.follower, new_acc);
+				await this.userFollowingService.unfollow(following.follower, old_acc);
+			} catch {
+				/* empty */
+			}
+		});
+
+		return 'ok';
+	}
 }
diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index b250b796d6..0b22aa9bcf 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -25,7 +25,7 @@ import { CustomEmojiService } from '@/core/CustomEmojiService.js';
 import { isNotNull } from '@/misc/is-not-null.js';
 import { LdSignatureService } from './LdSignatureService.js';
 import { ApMfmService } from './ApMfmService.js';
-import type { IAccept, IActivity, IAdd, IAnnounce, IApDocument, IApEmoji, IApHashtag, IApImage, IApMention, IBlock, ICreate, IDelete, IFlag, IFollow, IKey, ILike, IObject, IPost, IQuestion, IReject, IRemove, ITombstone, IUndo, IUpdate } from './type.js';
+import type { IAccept, IActivity, IAdd, IAnnounce, IApDocument, IApEmoji, IApHashtag, IApImage, IApMention, IBlock, ICreate, IDelete, IFlag, IFollow, IKey, ILike, IMove, IObject, IPost, IQuestion, IReject, IRemove, ITombstone, IUndo, IUpdate } from './type.js';
 import type { IIdentifier } from './models/identifier.js';
 
 @Injectable()
@@ -293,6 +293,22 @@ export class ApRendererService {
 	}
 
 	@bindThis
+	public renderMove(
+		src: { id: User['id']; host: User['host']; uri: User['host'] },
+		dst: { id: User['id']; host: User['host']; uri: User['host'] },
+	): IMove {
+		const actor = this.userEntityService.isLocalUser(src) ? `${this.config.url}/users/${src.id}` : src.uri!;
+		const target = this.userEntityService.isLocalUser(dst) ? `${this.config.url}/users/${dst.id}` : dst.uri!;
+		return {
+			id: `${this.config.url}/moves/${src.id}/${dst.id}`,
+			actor,
+			type: 'Move',
+			object: actor,
+			target,
+		};
+	}
+
+	@bindThis
 	public async renderNote(note: Note, dive = true): Promise<IPost> {
 		const getPromisedFiles = async (ids: string[]) => {
 			if (!ids || ids.length === 0) return [];
@@ -498,6 +514,14 @@ export class ApRendererService {
 			attachment: attachment.length ? attachment : undefined,
 		} as any;
 
+		if (user.movedToUri) {
+			person.movedTo = user.movedToUri;
+		}
+
+		if (user.alsoKnownAs) {
+			person.alsoKnownAs = user.alsoKnownAs;
+		}
+
 		if (profile.birthday) {
 			person['vcard:bday'] = profile.birthday;
 		}
diff --git a/packages/backend/src/core/activitypub/models/ApPersonService.ts b/packages/backend/src/core/activitypub/models/ApPersonService.ts
index 664e7eb4ea..21797cfcb7 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -281,6 +281,8 @@ export class ApPersonService implements OnModuleInit {
 					lastFetchedAt: new Date(),
 					name: truncate(person.name, nameLength),
 					isLocked: !!person.manuallyApprovesFollowers,
+					movedToUri: person.movedTo,
+					alsoKnownAs: person.alsoKnownAs,
 					isExplorable: !!person.discoverable,
 					username: person.preferredUsername,
 					usernameLower: person.preferredUsername!.toLowerCase(),
@@ -473,6 +475,8 @@ export class ApPersonService implements OnModuleInit {
 			isBot: getApType(object) === 'Service',
 			isCat: (person as any).isCat === true,
 			isLocked: !!person.manuallyApprovesFollowers,
+			movedToUri: person.movedTo ?? null,
+			alsoKnownAs: person.alsoKnownAs ?? null,
 			isExplorable: !!person.discoverable,
 		} as Partial<User>;
 
diff --git a/packages/backend/src/core/activitypub/type.ts b/packages/backend/src/core/activitypub/type.ts
index 8851946330..625135da6c 100644
--- a/packages/backend/src/core/activitypub/type.ts
+++ b/packages/backend/src/core/activitypub/type.ts
@@ -157,6 +157,8 @@ export interface IActor extends IObject {
 	name?: string;
 	preferredUsername?: string;
 	manuallyApprovesFollowers?: boolean;
+	movedTo?: string;
+	alsoKnownAs?: string[];
 	discoverable?: boolean;
 	inbox: string;
 	sharedInbox?: string;	// 後方互換性のため
@@ -300,6 +302,11 @@ export interface IFlag extends IActivity {
 	type: 'Flag';
 }
 
+export interface IMove extends IActivity {
+	type: 'Move';
+	target: IObject | string;
+}
+
 export const isCreate = (object: IObject): object is ICreate => getApType(object) === 'Create';
 export const isDelete = (object: IObject): object is IDelete => getApType(object) === 'Delete';
 export const isUpdate = (object: IObject): object is IUpdate => getApType(object) === 'Update';
@@ -314,3 +321,4 @@ export const isLike = (object: IObject): object is ILike => getApType(object) ==
 export const isAnnounce = (object: IObject): object is IAnnounce => getApType(object) === 'Announce';
 export const isBlock = (object: IObject): object is IBlock => getApType(object) === 'Block';
 export const isFlag = (object: IObject): object is IFlag => getApType(object) === 'Flag';
+export const isMove = (object: IObject): object is IMove => getApType(object) === 'Move';
diff --git a/packages/backend/src/core/entities/UserEntityService.ts b/packages/backend/src/core/entities/UserEntityService.ts
index cbe94451cc..e02f7535d4 100644
--- a/packages/backend/src/core/entities/UserEntityService.ts
+++ b/packages/backend/src/core/entities/UserEntityService.ts
@@ -15,6 +15,7 @@ import { birthdaySchema, descriptionSchema, localUsernameSchema, locationSchema,
 import type { UsersRepository, UserSecurityKeysRepository, FollowingsRepository, FollowRequestsRepository, BlockingsRepository, MutingsRepository, DriveFilesRepository, NoteUnreadsRepository, ChannelFollowingsRepository, UserNotePiningsRepository, UserProfilesRepository, InstancesRepository, AnnouncementReadsRepository, AnnouncementsRepository, PagesRepository, UserProfile, RenoteMutingsRepository } from '@/models/index.js';
 import { bindThis } from '@/decorators.js';
 import { RoleService } from '@/core/RoleService.js';
+import { ApPersonService } from '@/core/activitypub/models/ApPersonService.js';
 import { FederatedInstanceService } from '@/core/FederatedInstanceService.js';
 import type { OnModuleInit } from '@nestjs/common';
 import type { AntennaService } from '../AntennaService.js';
@@ -25,7 +26,7 @@ import type { PageEntityService } from './PageEntityService.js';
 
 type IsUserDetailed<Detailed extends boolean> = Detailed extends true ? Packed<'UserDetailed'> : Packed<'UserLite'>;
 type IsMeAndIsUserDetailed<ExpectsMe extends boolean | null, Detailed extends boolean> =
-	Detailed extends true ? 
+	Detailed extends true ?
 		ExpectsMe extends true ? Packed<'MeDetailed'> :
 		ExpectsMe extends false ? Packed<'UserDetailedNotMe'> :
 		Packed<'UserDetailed'> :
@@ -47,6 +48,7 @@ function isRemoteUser(user: User | { host: User['host'] }): boolean {
 
 @Injectable()
 export class UserEntityService implements OnModuleInit {
+	private apPersonService: ApPersonService;
 	private noteEntityService: NoteEntityService;
 	private driveFileEntityService: DriveFileEntityService;
 	private pageEntityService: PageEntityService;
@@ -122,6 +124,7 @@ export class UserEntityService implements OnModuleInit {
 	}
 
 	onModuleInit() {
+		this.apPersonService = this.moduleRef.get('ApPersonService');
 		this.noteEntityService = this.moduleRef.get('NoteEntityService');
 		this.driveFileEntityService = this.moduleRef.get('DriveFileEntityService');
 		this.pageEntityService = this.moduleRef.get('PageEntityService');
@@ -237,7 +240,7 @@ export class UserEntityService implements OnModuleInit {
 	@bindThis
 	public async getHasUnreadNotification(userId: User['id']): Promise<boolean> {
 		const latestReadNotificationId = await this.redisClient.get(`latestReadNotification:${userId}`);
-		
+
 		const latestNotificationIdsRes = await this.redisClient.xrevrange(
 			`notificationTimeline:${userId}`,
 			'+',
@@ -363,6 +366,8 @@ export class UserEntityService implements OnModuleInit {
 			...(opts.detail ? {
 				url: profile!.url,
 				uri: user.uri,
+				movedToUri: user.movedToUri ? await this.apPersonService.resolvePerson(user.movedToUri) : null,
+				alsoKnownAs: user.alsoKnownAs,
 				createdAt: user.createdAt.toISOString(),
 				updatedAt: user.updatedAt ? user.updatedAt.toISOString() : null,
 				lastFetchedAt: user.lastFetchedAt ? user.lastFetchedAt.toISOString() : null,
diff --git a/packages/backend/src/models/entities/User.ts b/packages/backend/src/models/entities/User.ts
index ca53c57d5a..04dfa21107 100644
--- a/packages/backend/src/models/entities/User.ts
+++ b/packages/backend/src/models/entities/User.ts
@@ -68,6 +68,19 @@ export class User {
 	})
 	public followingCount: number;
 
+	@Column('varchar', {
+		length: 512,
+		nullable: true,
+		comment: 'The URI of the new account of the User',
+	})
+	public movedToUri: string | null;
+
+	@Column('simple-array', {
+		nullable: true,
+		comment: 'URIs the user is known as too',
+	})
+	public alsoKnownAs: string[] | null;
+
 	@Column('integer', {
 		default: 0,
 		comment: 'The count of notes.',
diff --git a/packages/backend/src/models/json-schema/user.ts b/packages/backend/src/models/json-schema/user.ts
index e388a77a5e..7d40979e3d 100644
--- a/packages/backend/src/models/json-schema/user.ts
+++ b/packages/backend/src/models/json-schema/user.ts
@@ -72,6 +72,18 @@ export const packedUserDetailedNotMeOnlySchema = {
 			format: 'uri',
 			nullable: true, optional: false,
 		},
+		movedToUri: {
+			type: 'string',
+			format: 'uri',
+			nullable: true,
+			optional: false,
+		},
+		alsoKnownAs: {
+			type: 'array',
+			format: 'uri',
+			nullable: true,
+			optional: false,
+		},
 		createdAt: {
 			type: 'string',
 			nullable: false, optional: false,
diff --git a/packages/backend/src/server/api/EndpointsModule.ts b/packages/backend/src/server/api/EndpointsModule.ts
index cab2477414..5a53b3faf7 100644
--- a/packages/backend/src/server/api/EndpointsModule.ts
+++ b/packages/backend/src/server/api/EndpointsModule.ts
@@ -220,6 +220,8 @@ import * as ep___i_signinHistory from './endpoints/i/signin-history.js';
 import * as ep___i_unpin from './endpoints/i/unpin.js';
 import * as ep___i_updateEmail from './endpoints/i/update-email.js';
 import * as ep___i_update from './endpoints/i/update.js';
+import * as ep___i_move from './endpoints/i/move.js';
+import * as ep___i_knownAs from './endpoints/i/known-as.js';
 import * as ep___i_webhooks_create from './endpoints/i/webhooks/create.js';
 import * as ep___i_webhooks_show from './endpoints/i/webhooks/show.js';
 import * as ep___i_webhooks_list from './endpoints/i/webhooks/list.js';
@@ -551,6 +553,8 @@ const $i_signinHistory: Provider = { provide: 'ep:i/signin-history', useClass: e
 const $i_unpin: Provider = { provide: 'ep:i/unpin', useClass: ep___i_unpin.default };
 const $i_updateEmail: Provider = { provide: 'ep:i/update-email', useClass: ep___i_updateEmail.default };
 const $i_update: Provider = { provide: 'ep:i/update', useClass: ep___i_update.default };
+const $i_move: Provider = { provide: 'ep:i/move', useClass: ep___i_move.default };
+const $i_knownAs: Provider = { provide: 'ep:i/known-as', useClass: ep___i_knownAs.default };
 const $i_webhooks_create: Provider = { provide: 'ep:i/webhooks/create', useClass: ep___i_webhooks_create.default };
 const $i_webhooks_list: Provider = { provide: 'ep:i/webhooks/list', useClass: ep___i_webhooks_list.default };
 const $i_webhooks_show: Provider = { provide: 'ep:i/webhooks/show', useClass: ep___i_webhooks_show.default };
@@ -886,6 +890,8 @@ const $retention: Provider = { provide: 'ep:retention', useClass: ep___retention
 		$i_unpin,
 		$i_updateEmail,
 		$i_update,
+		$i_move,
+		$i_knownAs,
 		$i_webhooks_create,
 		$i_webhooks_list,
 		$i_webhooks_show,
@@ -1215,6 +1221,8 @@ const $retention: Provider = { provide: 'ep:retention', useClass: ep___retention
 		$i_unpin,
 		$i_updateEmail,
 		$i_update,
+		$i_move,
+		$i_knownAs,
 		$i_webhooks_create,
 		$i_webhooks_list,
 		$i_webhooks_show,
diff --git a/packages/backend/src/server/api/endpoints.ts b/packages/backend/src/server/api/endpoints.ts
index e33c2349cd..c8375ca149 100644
--- a/packages/backend/src/server/api/endpoints.ts
+++ b/packages/backend/src/server/api/endpoints.ts
@@ -220,6 +220,8 @@ import * as ep___i_signinHistory from './endpoints/i/signin-history.js';
 import * as ep___i_unpin from './endpoints/i/unpin.js';
 import * as ep___i_updateEmail from './endpoints/i/update-email.js';
 import * as ep___i_update from './endpoints/i/update.js';
+import * as ep___i_move from './endpoints/i/move.js';
+import * as ep___i_knownAs from './endpoints/i/known-as.js';
 import * as ep___i_webhooks_create from './endpoints/i/webhooks/create.js';
 import * as ep___i_webhooks_show from './endpoints/i/webhooks/show.js';
 import * as ep___i_webhooks_list from './endpoints/i/webhooks/list.js';
@@ -549,6 +551,8 @@ const eps = [
 	['i/unpin', ep___i_unpin],
 	['i/update-email', ep___i_updateEmail],
 	['i/update', ep___i_update],
+	['i/move', ep___i_move],
+	['i/known-as', ep___i_knownAs],
 	['i/webhooks/create', ep___i_webhooks_create],
 	['i/webhooks/list', ep___i_webhooks_list],
 	['i/webhooks/show', ep___i_webhooks_show],
diff --git a/packages/backend/src/server/api/endpoints/i/known-as.ts b/packages/backend/src/server/api/endpoints/i/known-as.ts
new file mode 100644
index 0000000000..964704d82b
--- /dev/null
+++ b/packages/backend/src/server/api/endpoints/i/known-as.ts
@@ -0,0 +1,92 @@
+import { Injectable } from '@nestjs/common';
+import ms from 'ms';
+
+import { User } from '@/models/entities/User.js';
+import { Endpoint } from '@/server/api/endpoint-base.js';
+import { ApiError } from '@/server/api/error.js';
+
+import { AccountMoveService } from '@/core/AccountMoveService.js';
+import { RemoteUserResolveService } from '@/core/RemoteUserResolveService.js';
+import { UserEntityService } from '@/core/entities/UserEntityService.js';
+import { ApiLoggerService } from '@/server/api/ApiLoggerService.js';
+
+export const meta = {
+	tags: ['users'],
+
+	secure: true,
+	requireCredential: true,
+
+	limit: {
+		duration: ms('1day'),
+		max: 30,
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5',
+		},
+		notRemote: {
+			message: 'User is not remote. You can only migrate from other instances.',
+			code: 'NOT_REMOTE',
+			id: '4362f8dc-731f-4ad8-a694-be2a88922a24',
+		},
+		uriNull: {
+			message: 'User ActivityPup URI is null.',
+			code: 'URI_NULL',
+			id: 'bf326f31-d430-4f97-9933-5d61e4d48a23',
+		},
+	},
+} as const;
+
+export const paramDef = {
+	type: 'object',
+	properties: {
+		alsoKnownAs: { type: 'string' },
+	},
+	required: ['alsoKnownAs'],
+} as const;
+
+@Injectable()
+export default class extends Endpoint<typeof meta, typeof paramDef> {
+	constructor(
+		private userEntityService: UserEntityService,
+		private remoteUserResolveService: RemoteUserResolveService,
+		private apiLoggerService: ApiLoggerService,
+		private accountMoveService: AccountMoveService,
+	) {
+		super(meta, paramDef, async (ps, me) => {
+			// Check parameter
+			if (!ps.alsoKnownAs) throw new ApiError(meta.errors.noSuchUser);
+
+			let unfiltered = ps.alsoKnownAs;
+			const updates = {} as Partial<User>;
+
+			if (!unfiltered) {
+				updates.alsoKnownAs = null;
+			} else {
+				// Parse user's input into the old account
+				if (unfiltered.startsWith('acct:')) unfiltered = unfiltered.substring(5);
+				if (unfiltered.startsWith('@')) unfiltered = unfiltered.substring(1);
+				if (!unfiltered.includes('@')) throw new ApiError(meta.errors.notRemote);
+
+				const userAddress = unfiltered.split('@');
+				// Retrieve the old account
+				const knownAs = await this.remoteUserResolveService.resolveUser(userAddress[0], userAddress[1]).catch((e) => {
+					this.apiLoggerService.logger.warn(`failed to resolve remote user: ${e}`);
+					throw new ApiError(meta.errors.noSuchUser);
+				});
+
+				const toUrl: string | null = knownAs.uri;
+				if (!toUrl) throw new ApiError(meta.errors.uriNull);
+				// Only allow moving from a remote account
+				if (this.userEntityService.isLocalUser(knownAs)) throw new ApiError(meta.errors.notRemote);
+
+				updates.alsoKnownAs = updates.alsoKnownAs?.concat([toUrl]) ?? [toUrl];
+			}
+
+			return await this.accountMoveService.createAlias(me, updates);
+		});
+	}
+}
diff --git a/packages/backend/src/server/api/endpoints/i/move.ts b/packages/backend/src/server/api/endpoints/i/move.ts
new file mode 100644
index 0000000000..346d8f95bb
--- /dev/null
+++ b/packages/backend/src/server/api/endpoints/i/move.ts
@@ -0,0 +1,136 @@
+import { Inject, Injectable } from '@nestjs/common';
+import ms from 'ms';
+
+import type { Config } from '@/config.js';
+import { DI } from '@/di-symbols.js';
+
+import { Endpoint } from '@/server/api/endpoint-base.js';
+import { ApiError } from '@/server/api/error.js';
+
+import { AccountMoveService } from '@/core/AccountMoveService.js';
+import { RemoteUserResolveService } from '@/core/RemoteUserResolveService.js';
+import { UserEntityService } from '@/core/entities/UserEntityService.js';
+import { ApiLoggerService } from '@/server/api/ApiLoggerService.js';
+import { GetterService } from '@/server/api/GetterService.js';
+import { ApPersonService } from '@/core/activitypub/models/ApPersonService.js';
+
+export const meta = {
+	tags: ['users'],
+
+	secure: true,
+	requireCredential: true,
+	limit: {
+		duration: ms('1day'),
+		max: 5,
+	},
+
+	errors: {
+		noSuchMoveTarget: {
+			message: 'No such move target.',
+			code: 'NO_SUCH_MOVE_TARGET',
+			id: 'b5c90186-4ab0-49c8-9bba-a1f76c202ba4',
+		},
+		remoteAccountForbids: {
+			message:
+				'Remote account doesn\'t have proper \'Known As\' alias. Did you remember to set it?',
+			code: 'REMOTE_ACCOUNT_FORBIDS',
+			id: 'b5c90186-4ab0-49c8-9bba-a1f766282ba4',
+		},
+		notRemote: {
+			message: 'User is not remote. You can only migrate to other instances.',
+			code: 'NOT_REMOTE',
+			id: '4362f8dc-731f-4ad8-a694-be2a88922a24',
+		},
+		rootForbidden: {
+			message: 'The root cant migrate.',
+			code: 'NOT_ROOT_FORBIDDEN',
+			id: '4362e8dc-731f-4ad8-a694-be2a88922a24',
+		},
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5',
+		},
+		uriNull: {
+			message: 'User ActivityPup URI is null.',
+			code: 'URI_NULL',
+			id: 'bf326f31-d430-4f97-9933-5d61e4d48a23',
+		},
+		localUriNull: {
+			message: 'Local User ActivityPup URI is null.',
+			code: 'URI_NULL',
+			id: '95ba11b9-90e8-43a5-ba16-7acc1ab32e71',
+		},
+		alreadyMoved: {
+			message: 'Account was already moved to another account.',
+			code: 'ALREADY_MOVED',
+			id: 'b234a14e-9ebe-4581-8000-074b3c215962',
+		},
+	},
+} as const;
+
+export const paramDef = {
+	type: 'object',
+	properties: {
+		moveToAccount: { type: 'string' },
+	},
+	required: ['moveToAccount'],
+} as const;
+
+// eslint-disable-next-line import/no-default-export
+@Injectable()
+export default class extends Endpoint<typeof meta, typeof paramDef> {
+	constructor(
+		@Inject(DI.config)
+		private config: Config,
+
+		private userEntityService: UserEntityService,
+		private remoteUserResolveService: RemoteUserResolveService,
+		private apiLoggerService: ApiLoggerService,
+		private accountMoveService: AccountMoveService,
+		private getterService: GetterService,
+		private apPersonService: ApPersonService,
+	) {
+		super(meta, paramDef, async (ps, me) => {
+			// Check parameter
+			if (!ps.moveToAccount) throw new ApiError(meta.errors.noSuchMoveTarget);
+			// Abort if user is the root
+			if (me.isRoot) throw new ApiError(meta.errors.rootForbidden);
+			// Abort if user has already moved
+			if (me.movedToUri) throw new ApiError(meta.errors.alreadyMoved);
+
+			let unfiltered = ps.moveToAccount;
+			if (!unfiltered) throw new ApiError(meta.errors.noSuchMoveTarget);
+
+			// Parse user's input into the destination account
+			if (unfiltered.startsWith('acct:')) unfiltered = unfiltered.substring(5);
+			if (unfiltered.startsWith('@')) unfiltered = unfiltered.substring(1);
+			if (!unfiltered.includes('@')) throw new ApiError(meta.errors.notRemote);
+
+			const userAddress = unfiltered.split('@');
+			// Retrieve the destination account
+			const remoteMoveTo = await this.remoteUserResolveService.resolveUser(userAddress[0], userAddress[1]).catch((e) => {
+				this.apiLoggerService.logger.warn(`failed to resolve remote user: ${e}`);
+				throw new ApiError(meta.errors.noSuchMoveTarget);
+			});
+			const moveTo = await this.getterService.getRemoteUser(remoteMoveTo.id);
+			if (!moveTo.uri) throw new ApiError(meta.errors.uriNull);
+			await this.apPersonService.updatePerson(moveTo.uri);
+			// Only allow moving to a remote account
+			if (this.userEntityService.isLocalUser(moveTo)) throw new ApiError(meta.errors.notRemote);
+
+			let allowed = false;
+
+			const fromUrl = `${this.config.url}/users/${me.id}`;
+			// Make sure that the user has indicated the old account as an alias
+			moveTo.alsoKnownAs?.forEach((elem) => {
+				if (fromUrl.includes(elem)) allowed = true;
+			});
+
+			// Abort if unintended
+			if (!(allowed && moveTo.uri && fromUrl)) throw new ApiError(meta.errors.remoteAccountForbids);
+
+			return await this.accountMoveService.moveToRemote(me, moveTo);
+		});
+	}
+}