diff --git a/packages/backend/src/server/api/api-handler.ts b/packages/backend/src/server/api/api-handler.ts
index c22c868c8..956096367 100644
--- a/packages/backend/src/server/api/api-handler.ts
+++ b/packages/backend/src/server/api/api-handler.ts
@@ -34,7 +34,8 @@ export default (endpoint: IEndpoint, ctx: Koa.Context) => new Promise<void>((res
 	};
 
 	// Authentication
-	authenticate(body['i']).then(([user, app]) => {
+	// for GET requests, do not even pass on the body parameter as it is considered unsafe
+	authenticate(ctx.headers.authorization, ctx.method === 'GET' ? null : body['i']).then(([user, app]) => {
 		// API invoking
 		call(endpoint.name, user, app, body, ctx).then((res: any) => {
 			if (ctx.method === 'GET' && endpoint.meta.cacheSec && !body['i'] && !user) {
@@ -46,11 +47,15 @@ export default (endpoint: IEndpoint, ctx: Koa.Context) => new Promise<void>((res
 		});
 	}).catch(e => {
 		if (e instanceof AuthenticationError) {
-			reply(403, new ApiError({
-				message: 'Authentication failed. Please ensure your token is correct.',
+			ctx.response.status = 403;
+			ctx.response.set('WWW-Authenticate', 'Bearer');
+			ctx.response.body = {
+				message: 'Authentication failed: ' + e.message,
 				code: 'AUTHENTICATION_FAILED',
 				id: 'b0a7f5f8-dc2f-4171-b91f-de88ad238e14',
-			}));
+				kind: 'client',
+			};
+			res();
 		} else {
 			reply(500, new ApiError());
 		}
diff --git a/packages/backend/src/server/api/authenticate.ts b/packages/backend/src/server/api/authenticate.ts
index 65ccfcf55..39be06c29 100644
--- a/packages/backend/src/server/api/authenticate.ts
+++ b/packages/backend/src/server/api/authenticate.ts
@@ -15,8 +15,25 @@ export class AuthenticationError extends Error {
 	}
 }
 
-export default async (token: string | null): Promise<[CacheableLocalUser | null | undefined, AccessToken | null | undefined]> => {
-	if (token == null) {
+export default async (authorization: string | null | undefined, bodyToken: string | null): Promise<[CacheableLocalUser | null | undefined, AccessToken | null | undefined]> => {
+	let token: string | null = null;
+
+	// check if there is an authorization header set
+	if (authorization != null) {
+		if (bodyToken != null) {
+			throw new AuthenticationError('using multiple authorization schemes');
+		}
+
+		// check if OAuth 2.0 Bearer tokens are being used
+		// Authorization schemes are case insensitive
+		if (authorization.substring(0, 7).toLowerCase() === 'bearer ') {
+			token = authorization.substring(7);
+		} else {
+			throw new AuthenticationError('unsupported authentication scheme');
+		}
+	} else if (bodyToken != null) {
+		token = bodyToken;
+	} else {
 		return [null, null];
 	}
 
@@ -25,7 +42,7 @@ export default async (token: string | null): Promise<[CacheableLocalUser | null
 			() => Users.findOneBy({ token }) as Promise<ILocalUser | null>);
 
 		if (user == null) {
-			throw new AuthenticationError('user not found');
+			throw new AuthenticationError('unknown token');
 		}
 
 		return [user, null];
@@ -39,7 +56,7 @@ export default async (token: string | null): Promise<[CacheableLocalUser | null
 		});
 
 		if (accessToken == null) {
-			throw new AuthenticationError('invalid signature');
+			throw new AuthenticationError('unknown token');
 		}
 
 		AccessTokens.update(accessToken.id, {
diff --git a/packages/backend/src/server/api/openapi/gen-spec.ts b/packages/backend/src/server/api/openapi/gen-spec.ts
index 68fa81404..289bd8088 100644
--- a/packages/backend/src/server/api/openapi/gen-spec.ts
+++ b/packages/backend/src/server/api/openapi/gen-spec.ts
@@ -15,7 +15,7 @@ export function genOpenapiSpec() {
 
 		externalDocs: {
 			description: 'Repository',
-			url: 'https://github.com/misskey-dev/misskey',
+			url: 'https://akkoma.dev/FoundKeyGang/FoundKey',
 		},
 
 		servers: [{
@@ -33,6 +33,11 @@ export function genOpenapiSpec() {
 					in: 'body',
 					name: 'i',
 				},
+				// TODO: change this to oauth2 when the remaining oauth stuff is set up
+				Bearer: {
+					type: 'http',
+					scheme: 'bearer',
+				}
 			},
 		},
 	};
@@ -71,22 +76,29 @@ export function genOpenapiSpec() {
 			schema.required.push('file');
 		}
 
+		const security = [
+			{
+				ApiKeyAuth: [],
+			},
+			{
+				Bearer: [],
+			},
+		];
+		if (!endpoint.meta.requireCredential) {
+			// add this to make authentication optional
+			security.push({});
+		}
+
 		const info = {
 			operationId: endpoint.name,
 			summary: endpoint.name,
 			description: desc,
 			externalDocs: {
 				description: 'Source code',
-				url: `https://github.com/misskey-dev/misskey/blob/develop/packages/backend/src/server/api/endpoints/${endpoint.name}.ts`,
+				url: `https://akkoma.dev/FoundKeyGang/FoundKey/src/branch/main/packages/backend/src/server/api/endpoints/${endpoint.name}.ts`,
 			},
-			...(endpoint.meta.tags ? {
-				tags: [endpoint.meta.tags[0]],
-			} : {}),
-			...(endpoint.meta.requireCredential ? {
-				security: [{
-					ApiKeyAuth: [],
-				}],
-			} : {}),
+			tags: endpoint.meta.tags || undefined,
+			security,
 			requestBody: {
 				required: true,
 				content: {
@@ -181,9 +193,16 @@ export function genOpenapiSpec() {
 			},
 		};
 
-		spec.paths['/' + endpoint.name] = {
+		const path = {
 			post: info,
 		};
+		if (endpoint.meta.allowGet) {
+			path.get = { ...info };
+			// API Key authentication is not permitted for GET requests
+			path.get.security = path.get.security.filter(elem => !Object.prototype.hasOwnProperty.call(elem, 'ApiKeyAuth'));
+		}
+
+		spec.paths['/' + endpoint.name] = path;
 	}
 
 	return spec;
diff --git a/packages/backend/src/server/api/streaming.ts b/packages/backend/src/server/api/streaming.ts
index f8e42d27f..cfe209d09 100644
--- a/packages/backend/src/server/api/streaming.ts
+++ b/packages/backend/src/server/api/streaming.ts
@@ -17,10 +17,14 @@ export const initializeStreamingServer = (server: http.Server) => {
 	ws.on('request', async (request) => {
 		const q = request.resourceURL.query as ParsedUrlQuery;
 
-		// TODO: トークンが間違ってるなどしてauthenticateに失敗したら
-		// コネクション切断するなりエラーメッセージ返すなりする
-		// (現状はエラーがキャッチされておらずサーバーのログに流れて邪魔なので)
-		const [user, app] = await authenticate(q.i as string);
+		const [user, app] = await authenticate(request.httpRequest.headers.authorization, q.i)
+			.catch(err => {
+				request.reject(403, err.message);
+				return [];
+			});
+		if (typeof user === 'undefined') {
+			return;
+		}
 
 		if (user?.isSuspended) {
 			request.reject(400);
diff --git a/packages/client/src/components/cropper-dialog.vue b/packages/client/src/components/cropper-dialog.vue
index a8bde6ea0..47335af6a 100644
--- a/packages/client/src/components/cropper-dialog.vue
+++ b/packages/client/src/components/cropper-dialog.vue
@@ -62,7 +62,6 @@ const ok = async () => {
 		croppedCanvas.toBlob(blob => {
 			const formData = new FormData();
 			formData.append('file', blob);
-			formData.append('i', $i.token);
 			if (defaultStore.state.uploadFolder) {
 				formData.append('folderId', defaultStore.state.uploadFolder);
 			}
@@ -70,6 +69,9 @@ const ok = async () => {
 			fetch(apiUrl + '/drive/files/create', {
 				method: 'POST',
 				body: formData,
+				headers: {
+					authorization: `Bearer ${$i.token}`,
+				},
 			})
 			.then(response => response.json())
 			.then(f => {
diff --git a/packages/client/src/components/page/page.post.vue b/packages/client/src/components/page/page.post.vue
index 3401f945b..1b11e6f48 100644
--- a/packages/client/src/components/page/page.post.vue
+++ b/packages/client/src/components/page/page.post.vue
@@ -54,7 +54,6 @@ export default defineComponent({
 				canvas.toBlob(blob => {
 					const formData = new FormData();
 					formData.append('file', blob);
-					formData.append('i', this.$i.token);
 					if (this.$store.state.uploadFolder) {
 						formData.append('folderId', this.$store.state.uploadFolder);
 					}
@@ -62,6 +61,9 @@ export default defineComponent({
 					fetch(apiUrl + '/drive/files/create', {
 						method: 'POST',
 						body: formData,
+						headers: {
+							authorization: `Bearer ${this.$i.token}`,
+						},
 					})
 					.then(response => response.json())
 					.then(f => {
diff --git a/packages/client/src/os.ts b/packages/client/src/os.ts
index 64fb9b0ea..fa7c41357 100644
--- a/packages/client/src/os.ts
+++ b/packages/client/src/os.ts
@@ -23,17 +23,16 @@ export const api = ((endpoint: string, data: Record<string, any> = {}, token?: s
 		pendingApiRequestsCount.value--;
 	};
 
-	const promise = new Promise((resolve, reject) => {
-		// Append a credential
-		if ($i) (data as any).i = $i.token;
-		if (token !== undefined) (data as any).i = token;
+	const authorizationToken = token ?? $i?.token ?? undefined;
+	const authorization = authorizationToken ? `Bearer ${authorizationToken}` : undefined;
 
-		// Send request
+	const promise = new Promise((resolve, reject) => {
 		fetch(endpoint.indexOf('://') > -1 ? endpoint : `${apiUrl}/${endpoint}`, {
 			method: 'POST',
 			body: JSON.stringify(data),
 			credentials: 'omit',
 			cache: 'no-cache',
+			headers: { authorization },
 		}).then(async (res) => {
 			const body = res.status === 204 ? null : await res.json();
 
@@ -52,7 +51,7 @@ export const api = ((endpoint: string, data: Record<string, any> = {}, token?: s
 	return promise;
 }) as typeof apiClient.request;
 
-export const apiGet = ((endpoint: string, data: Record<string, any> = {}) => {
+export const apiGet = ((endpoint: string, data: Record<string, any> = {}, token?: string | null | undefined) => {
 	pendingApiRequestsCount.value++;
 
 	const onFinally = () => {
@@ -61,12 +60,16 @@ export const apiGet = ((endpoint: string, data: Record<string, any> = {}) => {
 
 	const query = new URLSearchParams(data);
 
+	const authorizationToken = token ?? $i?.token ?? undefined;
+	const authorization = authorizationToken ? `Bearer ${authorizationToken}` : undefined;
+
 	const promise = new Promise((resolve, reject) => {
 		// Send request
 		fetch(`${apiUrl}/${endpoint}?${query}`, {
 			method: 'GET',
 			credentials: 'omit',
 			cache: 'default',
+			headers: { authorization },
 		}).then(async (res) => {
 			const body = res.status === 204 ? null : await res.json();
 
diff --git a/packages/client/src/scripts/upload.ts b/packages/client/src/scripts/upload.ts
index 2f7b30b58..c333826ce 100644
--- a/packages/client/src/scripts/upload.ts
+++ b/packages/client/src/scripts/upload.ts
@@ -70,7 +70,6 @@ export function uploadFile(
 			}
 
 			const formData = new FormData();
-			formData.append('i', $i.token);
 			formData.append('force', 'true');
 			formData.append('file', resizedImage || file);
 			formData.append('name', ctx.name);
@@ -78,6 +77,7 @@ export function uploadFile(
 
 			const xhr = new XMLHttpRequest();
 			xhr.open('POST', apiUrl + '/drive/files/create', true);
+			xhr.setRequestHeader('Authorization', `Bearer ${$i.token}`);
 			xhr.onload = (ev) => {
 				if (xhr.status !== 200 || ev.target == null || ev.target.response == null) {
 					// TODO: 消すのではなくて再送できるようにしたい