diff --git a/packages/backend/src/server/api/ApiCallService.ts b/packages/backend/src/server/api/ApiCallService.ts
index 45fb473763..09e3724394 100644
--- a/packages/backend/src/server/api/ApiCallService.ts
+++ b/packages/backend/src/server/api/ApiCallService.ts
@@ -53,44 +53,72 @@ export class ApiCallService implements OnApplicationShutdown {
 		}, 1000 * 60 * 60);
 	}
 
+	#sendApiError(reply: FastifyReply, err: ApiError): void {
+		let statusCode = err.httpStatusCode;
+		if (err.httpStatusCode === 401) {
+			reply.header('WWW-Authenticate', 'Bearer realm="Misskey"');
+		} else if (err.kind === 'client') {
+			reply.header('WWW-Authenticate', `Bearer realm="Misskey", error="invalid_request", error_description="${err.message}"`);
+			statusCode = statusCode ?? 400;
+		} else if (err.kind === 'permission') {
+			// (ROLE_PERMISSION_DENIEDは関係ない)
+			if (err.code === 'PERMISSION_DENIED') {
+				reply.header('WWW-Authenticate', `Bearer realm="Misskey", error="insufficient_scope", error_description="${err.message}"`);
+			}
+			statusCode = statusCode ?? 403;
+		} else if (!statusCode) {
+			statusCode = 500;
+		}
+		this.send(reply, statusCode, err);
+	}
+
+	#sendAuthenticationError(reply: FastifyReply, err: unknown): void {
+		if (err instanceof AuthenticationError) {
+			const message = 'Authentication failed. Please ensure your token is correct.';
+			reply.header('WWW-Authenticate', `Bearer realm="Misskey", error="invalid_token", error_description="${message}"`);
+			this.send(reply, 401, new ApiError({
+				message: 'Authentication failed. Please ensure your token is correct.',
+				code: 'AUTHENTICATION_FAILED',
+				id: 'b0a7f5f8-dc2f-4171-b91f-de88ad238e14',
+			}));
+		} else {
+			this.send(reply, 500, new ApiError());
+		}
+	}
+
 	@bindThis
 	public handleRequest(
 		endpoint: IEndpoint & { exec: any },
 		request: FastifyRequest<{ Body: Record<string, unknown> | undefined, Querystring: Record<string, unknown> }>,
 		reply: FastifyReply,
-	) {
+	): void {
 		const body = request.method === 'GET'
 			? request.query
 			: request.body;
 
-		const token = body?.['i'];
+		// https://datatracker.ietf.org/doc/html/rfc6750.html#section-2.1 (case sensitive)
+		const token = request.headers.authorization?.startsWith('Bearer ')
+			? request.headers.authorization.slice(7)
+			: body?.['i'];
 		if (token != null && typeof token !== 'string') {
 			reply.code(400);
 			return;
 		}
 		this.authenticateService.authenticate(token).then(([user, app]) => {
 			this.call(endpoint, user, app, body, null, request).then((res) => {
-				if (request.method === 'GET' && endpoint.meta.cacheSec && !body?.['i'] && !user) {
+				if (request.method === 'GET' && endpoint.meta.cacheSec && !token && !user) {
 					reply.header('Cache-Control', `public, max-age=${endpoint.meta.cacheSec}`);
 				}
 				this.send(reply, res);
 			}).catch((err: ApiError) => {
-				this.send(reply, err.httpStatusCode ? err.httpStatusCode : err.kind === 'client' ? 400 : err.kind === 'permission' ? 403 : 500, err);
+				this.#sendApiError(reply, err);
 			});
 
 			if (user) {
 				this.logIp(request, user);
 			}
 		}).catch(err => {
-			if (err instanceof AuthenticationError) {
-				this.send(reply, 401, new ApiError({
-					message: 'Authentication failed. Please ensure your token is correct.',
-					code: 'AUTHENTICATION_FAILED',
-					id: 'b0a7f5f8-dc2f-4171-b91f-de88ad238e14',
-				}));
-			} else {
-				this.send(reply, 500, new ApiError());
-			}
+			this.#sendAuthenticationError(reply, err);
 		});
 	}
 
@@ -99,7 +127,7 @@ export class ApiCallService implements OnApplicationShutdown {
 		endpoint: IEndpoint & { exec: any },
 		request: FastifyRequest<{ Body: Record<string, unknown>, Querystring: Record<string, unknown> }>,
 		reply: FastifyReply,
-	) {
+	): Promise<void> {
 		const multipartData = await request.file().catch(() => {
 			/* Fastify throws if the remote didn't send multipart data. Return 400 below. */
 		});
@@ -117,7 +145,10 @@ export class ApiCallService implements OnApplicationShutdown {
 			fields[k] = typeof v === 'object' && 'value' in v ? v.value : undefined;
 		}
 
-		const token = fields['i'];
+		// https://datatracker.ietf.org/doc/html/rfc6750.html#section-2.1 (case sensitive)
+		const token = request.headers.authorization?.startsWith('Bearer ')
+			? request.headers.authorization.slice(7)
+			: fields['i'];
 		if (token != null && typeof token !== 'string') {
 			reply.code(400);
 			return;
@@ -129,22 +160,14 @@ export class ApiCallService implements OnApplicationShutdown {
 			}, request).then((res) => {
 				this.send(reply, res);
 			}).catch((err: ApiError) => {
-				this.send(reply, err.httpStatusCode ? err.httpStatusCode : err.kind === 'client' ? 400 : err.kind === 'permission' ? 403 : 500, err);
+				this.#sendApiError(reply, err);
 			});
 
 			if (user) {
 				this.logIp(request, user);
 			}
 		}).catch(err => {
-			if (err instanceof AuthenticationError) {
-				this.send(reply, 401, new ApiError({
-					message: 'Authentication failed. Please ensure your token is correct.',
-					code: 'AUTHENTICATION_FAILED',
-					id: 'b0a7f5f8-dc2f-4171-b91f-de88ad238e14',
-				}));
-			} else {
-				this.send(reply, 500, new ApiError());
-			}
+			this.#sendAuthenticationError(reply, err);
 		});
 	}
 
@@ -213,7 +236,7 @@ export class ApiCallService implements OnApplicationShutdown {
 		}
 
 		if (ep.meta.limit) {
-		// koa will automatically load the `X-Forwarded-For` header if `proxy: true` is configured in the app.
+			// koa will automatically load the `X-Forwarded-For` header if `proxy: true` is configured in the app.
 			let limitActor: string;
 			if (user) {
 				limitActor = user.id;
@@ -255,8 +278,8 @@ export class ApiCallService implements OnApplicationShutdown {
 				throw new ApiError({
 					message: 'Your account has been suspended.',
 					code: 'YOUR_ACCOUNT_SUSPENDED',
+					kind: 'permission',
 					id: 'a8c724b3-6e9c-4b46-b1a8-bc3ed6258370',
-					httpStatusCode: 403,
 				});
 			}
 		}
@@ -266,8 +289,8 @@ export class ApiCallService implements OnApplicationShutdown {
 				throw new ApiError({
 					message: 'You have moved your account.',
 					code: 'YOUR_ACCOUNT_MOVED',
+					kind: 'permission',
 					id: '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31',
-					httpStatusCode: 403,
 				});
 			}
 		}
@@ -321,7 +344,7 @@ export class ApiCallService implements OnApplicationShutdown {
 					try {
 						data[k] = JSON.parse(data[k]);
 					} catch (e) {
-						throw	new ApiError({
+						throw new ApiError({
 							message: 'Invalid param.',
 							code: 'INVALID_PARAM',
 							id: '0b5f1631-7c1a-41a6-b399-cce335f34d85',
diff --git a/packages/backend/src/server/api/StreamingApiServerService.ts b/packages/backend/src/server/api/StreamingApiServerService.ts
index 8f2e51d584..4a0342d2b4 100644
--- a/packages/backend/src/server/api/StreamingApiServerService.ts
+++ b/packages/backend/src/server/api/StreamingApiServerService.ts
@@ -58,11 +58,21 @@ export class StreamingApiServerService {
 			let user: LocalUser | null = null;
 			let app: AccessToken | null = null;
 
+			// https://datatracker.ietf.org/doc/html/rfc6750.html#section-2.1
+			// Note that the standard WHATWG WebSocket API does not support setting any headers,
+			// but non-browser apps may still be able to set it.
+			const token = request.headers.authorization?.startsWith('Bearer ')
+				? request.headers.authorization.slice(7)
+				: q.get('i');
+
 			try {
-				[user, app] = await this.authenticateService.authenticate(q.get('i'));
+				[user, app] = await this.authenticateService.authenticate(token);
 			} catch (e) {
 				if (e instanceof AuthenticationError) {
-					socket.write('HTTP/1.1 401 Unauthorized\r\n\r\n');
+					socket.write([
+						'HTTP/1.1 401 Unauthorized',
+						'WWW-Authenticate: Bearer realm="Misskey", error="invalid_token", error_description="Failed to authenticate"',
+					].join('\r\n') + '\r\n\r\n');
 				} else {
 					socket.write('HTTP/1.1 500 Internal Server Error\r\n\r\n');
 				}
diff --git a/packages/backend/test/e2e/api.ts b/packages/backend/test/e2e/api.ts
index 4b9167b6b1..c6beec4f88 100644
--- a/packages/backend/test/e2e/api.ts
+++ b/packages/backend/test/e2e/api.ts
@@ -1,9 +1,10 @@
 process.env.NODE_ENV = 'test';
 
 import * as assert from 'assert';
-import { signup, api, startServer, successfulApiCall, failedApiCall } from '../utils.js';
+import { signup, api, startServer, successfulApiCall, failedApiCall, uploadFile, waitFire, connectStream } from '../utils.js';
 import type { INestApplicationContext } from '@nestjs/common';
 import type * as misskey from 'misskey-js';
+import { IncomingMessage } from 'http';
 
 describe('API', () => {
 	let app: INestApplicationContext;
@@ -123,4 +124,100 @@ describe('API', () => {
 			id: 'b0a7f5f8-dc2f-4171-b91f-de88ad238e14',
 		});
 	});
+
+	describe('Authentication header', () => {
+		test('一般リクエスト', async () => {
+			await successfulApiCall({
+				endpoint: '/admin/get-index-stats',
+				parameters: {},
+				user: {
+					token: alice.token,
+					bearer: true,
+				},
+			});
+		});
+
+		test('multipartリクエスト', async () => {
+			const result = await uploadFile({
+				token: alice.token,
+				bearer: true,
+			});
+			assert.strictEqual(result.status, 200);
+		});
+
+		test('streaming', async () => {
+			const fired = await waitFire(
+				{
+					token: alice.token,
+					bearer: true,
+				},
+				'homeTimeline',
+				() => api('notes/create', { text: 'foo' }, alice),
+				msg => msg.type === 'note' && msg.body.text === 'foo',
+			);
+			assert.strictEqual(fired, true);
+		});
+	});
+
+	describe('tokenエラー応答でWWW-Authenticate headerを送る', () => {
+		describe('invalid_token', () => {
+			test('一般リクエスト', async () => {
+				const result = await api('/admin/get-index-stats', {}, {
+					token: 'syuilo',
+					bearer: true,
+				});
+				assert.strictEqual(result.status, 401);
+				assert.ok(result.headers.get('WWW-Authenticate')?.startsWith('Bearer realm="Misskey", error="invalid_token", error_description'));
+			});
+
+			test('multipartリクエスト', async () => {
+				const result = await uploadFile({
+					token: 'syuilo',
+					bearer: true,
+				});
+				assert.strictEqual(result.status, 401);
+				assert.ok(result.headers.get('WWW-Authenticate')?.startsWith('Bearer realm="Misskey", error="invalid_token", error_description'));
+			});
+
+			test('streaming', async () => {
+				await assert.rejects(connectStream(
+					{
+						token: 'syuilo',
+						bearer: true,
+					},
+					'homeTimeline',
+					() => { },
+				), (err: IncomingMessage) => {
+					assert.strictEqual(err.statusCode, 401);
+					assert.ok(err.headers['www-authenticate']?.startsWith('Bearer realm="Misskey", error="invalid_token", error_description'));
+					return true;
+				});
+			});
+		});
+
+		describe('tokenがないとrealmだけおくる', () => {
+			test('一般リクエスト', async () => {
+				const result = await api('/admin/get-index-stats', {});
+				assert.strictEqual(result.status, 401);
+				assert.strictEqual(result.headers.get('WWW-Authenticate'), 'Bearer realm="Misskey"');
+			});
+
+			test('multipartリクエスト', async () => {
+				const result = await uploadFile();
+				assert.strictEqual(result.status, 401);
+				assert.strictEqual(result.headers.get('WWW-Authenticate'), 'Bearer realm="Misskey"');
+			});
+		});
+
+		test('invalid_request', async () => {
+			const result = await api('/notes/create', { text: true }, {
+				token: alice.token,
+				bearer: true,
+			});
+			assert.strictEqual(result.status, 400);
+			assert.ok(result.headers.get('WWW-Authenticate')?.startsWith('Bearer realm="Misskey", error="invalid_request", error_description'));
+		});
+
+		// TODO: insufficient_scope test (authテストが全然なくて書けない)
+	});
 });
diff --git a/packages/backend/test/utils.ts b/packages/backend/test/utils.ts
index 8583f024cb..48947072e3 100644
--- a/packages/backend/test/utils.ts
+++ b/packages/backend/test/utils.ts
@@ -2,7 +2,7 @@ import * as assert from 'node:assert';
 import { readFile } from 'node:fs/promises';
 import { isAbsolute, basename } from 'node:path';
 import { inspect } from 'node:util';
-import WebSocket from 'ws';
+import WebSocket, { ClientOptions } from 'ws';
 import fetch, { Blob, File, RequestInit } from 'node-fetch';
 import { DataSource } from 'typeorm';
 import { JSDOM } from 'jsdom';
@@ -13,7 +13,10 @@ import type * as misskey from 'misskey-js';
 
 export { server as startServer } from '@/boot/common.js';
 
-interface UserToken { token: string }
+interface UserToken {
+	token: string;
+	bearer?: boolean;
+}
 
 const config = loadConfig();
 export const port = config.port;
@@ -57,27 +60,33 @@ export const failedApiCall = async <T, >(request: ApiRequest, assertion: {
 	return res.body;
 };
 
-const request = async (path: string, params: any, me?: UserToken): Promise<{ body: any, status: number }> => {
-	const auth = me ? {
-		i: me.token,
-	} : {};
+const request = async (path: string, params: any, me?: UserToken): Promise<{ status: number, headers: Headers, body: any }> => {
+	const bodyAuth: Record<string, string> = {};
+	const headers: Record<string, string> = {
+		'Content-Type': 'application/json',
+	};
+
+	if (me?.bearer) {
+		headers.Authorization = `Bearer ${me.token}`;
+	} else if (me) {
+		bodyAuth.i = me.token;
+	}
 
 	const res = await relativeFetch(path, {
 		method: 'POST',
-		headers: {
-			'Content-Type': 'application/json',
-		},
-		body: JSON.stringify(Object.assign(auth, params)),
+		headers,
+		body: JSON.stringify(Object.assign(bodyAuth, params)),
 		redirect: 'manual',
 	});
 
-	const status = res.status;
 	const body = res.headers.get('content-type') === 'application/json; charset=utf-8'
 		? await res.json()
 		: null;
 
 	return {
-		body, status,
+		status: res.status,
+		headers: res.headers,
+		body,
 	};
 };
 
@@ -241,7 +250,7 @@ interface UploadOptions {
  * Upload file
  * @param user User
  */
-export const uploadFile = async (user: UserToken, { path, name, blob }: UploadOptions = {}): Promise<any> => {
+export const uploadFile = async (user?: UserToken, { path, name, blob }: UploadOptions = {}): Promise<{ status: number, headers: Headers, body: misskey.Endpoints['drive/files/create']['res'] | null }> => {
 	const absPath = path == null
 		? new URL('resources/Lenna.jpg', import.meta.url)
 		: isAbsolute(path.toString())
@@ -249,7 +258,6 @@ export const uploadFile = async (user: UserToken, { path, name, blob }: UploadOp
 			: new URL(path, new URL('resources/', import.meta.url));
 
 	const formData = new FormData();
-	formData.append('i', user.token);
 	formData.append('file', blob ??
 		new File([await readFile(absPath)], basename(absPath.toString())));
 	formData.append('force', 'true');
@@ -257,15 +265,24 @@ export const uploadFile = async (user: UserToken, { path, name, blob }: UploadOp
 		formData.append('name', name);
 	}
 
+	const headers: Record<string, string> = {};
+	if (user?.bearer) {
+		headers.Authorization = `Bearer ${user.token}`;
+	} else if (user) {
+		formData.append('i', user.token);
+	}
+
 	const res = await relativeFetch('api/drive/files/create', {
 		method: 'POST',
 		body: formData,
+		headers,
 	});
 
-	const body = res.status !== 204 ? await res.json() : null;
+	const body = res.status !== 204 ? await res.json() as misskey.Endpoints['drive/files/create']['res'] : null;
 
 	return {
 		status: res.status,
+		headers: res.headers,
 		body,
 	};
 };
@@ -294,8 +311,16 @@ export const uploadUrl = async (user: UserToken, url: string) => {
 
 export function connectStream(user: UserToken, channel: string, listener: (message: Record<string, any>) => any, params?: any): Promise<WebSocket> {
 	return new Promise((res, rej) => {
-		const ws = new WebSocket(`ws://127.0.0.1:${port}/streaming?i=${user.token}`);
+		const url = new URL(`ws://127.0.0.1:${port}/streaming`);
+		const options: ClientOptions = {};
+		if (user.bearer) {
+			options.headers = { Authorization: `Bearer ${user.token}` };
+		} else {
+			url.searchParams.set('i', user.token);
+		}
+		const ws = new WebSocket(url, options);
 
+		ws.on('unexpected-response', (req, res) => rej(res));
 		ws.on('open', () => {
 			ws.on('message', data => {
 				const msg = JSON.parse(data.toString());
diff --git a/packages/misskey-js/etc/misskey-js.api.md b/packages/misskey-js/etc/misskey-js.api.md
index 5f292148ae..c9b3fd6056 100644
--- a/packages/misskey-js/etc/misskey-js.api.md
+++ b/packages/misskey-js/etc/misskey-js.api.md
@@ -960,8 +960,14 @@ export type Endpoints = {
         res: TODO;
     };
     'drive/files/create': {
-        req: TODO;
-        res: TODO;
+        req: {
+            folderId?: string;
+            name?: string;
+            comment?: string;
+            isSentisive?: boolean;
+            force?: boolean;
+        };
+        res: DriveFile;
     };
     'drive/files/delete': {
         req: {
@@ -2750,7 +2756,7 @@ type UserSorting = '+follower' | '-follower' | '+createdAt' | '-createdAt' | '+u
 //
 // src/api.types.ts:16:32 - (ae-forgotten-export) The symbol "TODO" needs to be exported by the entry point index.d.ts
 // src/api.types.ts:18:25 - (ae-forgotten-export) The symbol "NoParams" needs to be exported by the entry point index.d.ts
-// src/api.types.ts:611:18 - (ae-forgotten-export) The symbol "ShowUserReq" needs to be exported by the entry point index.d.ts
+// src/api.types.ts:620:18 - (ae-forgotten-export) The symbol "ShowUserReq" needs to be exported by the entry point index.d.ts
 // src/streaming.types.ts:33:4 - (ae-forgotten-export) The symbol "FIXME" needs to be exported by the entry point index.d.ts
 
 // (No @packageDocumentation comment for this package)
diff --git a/packages/misskey-js/src/api.types.ts b/packages/misskey-js/src/api.types.ts
index 293e0043b7..93f327e67e 100644
--- a/packages/misskey-js/src/api.types.ts
+++ b/packages/misskey-js/src/api.types.ts
@@ -262,7 +262,16 @@ export type Endpoints = {
 	'drive/files': { req: { folderId?: DriveFolder['id'] | null; type?: DriveFile['type'] | null; limit?: number; sinceId?: DriveFile['id']; untilId?: DriveFile['id']; }; res: DriveFile[]; };
 	'drive/files/attached-notes': { req: TODO; res: TODO; };
 	'drive/files/check-existence': { req: TODO; res: TODO; };
-	'drive/files/create': { req: TODO; res: TODO; };
+	'drive/files/create': {
+		req: {
+			folderId?: string,
+			name?: string,
+			comment?: string,
+			isSentisive?: boolean,
+			force?: boolean,
+		};
+		res: DriveFile;
+	};
 	'drive/files/delete': { req: { fileId: DriveFile['id']; }; res: null; };
 	'drive/files/find-by-hash': { req: TODO; res: TODO; };
 	'drive/files/find': { req: { name: string; folderId?: DriveFolder['id'] | null; }; res: DriveFile[]; };