refactor progress

packages/oauth2/package.json

@@ -0,0 +1,20 @@
+{
+	"name": "@fluxer/oauth2",
+	"version": "0.0.0",
+	"private": true,
+	"type": "module",
+	"exports": {
+		"./*": "./*"
+	},
+	"scripts": {
+		"test": "vitest run",
+		"test:watch": "vitest",
+		"typecheck": "tsgo --noEmit"
+	},
+	"devDependencies": {
+		"@types/node": "catalog:",
+		"@typescript/native-preview": "catalog:",
+		"vite-tsconfig-paths": "catalog:",
+		"vitest": "catalog:"
+	}
+}

packages/oauth2/src/OAuth2.tsx

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {randomBytes} from 'node:crypto';
+
+export interface OAuth2Config {
+	clientId: string;
+	clientSecret: string;
+	redirectUri: string;
+	authorizeEndpoint: string;
+	tokenEndpoint: string;
+	scope: string;
+}
+
+export function generateState(): string {
+	return randomBytes(32).toString('base64url');
+}
+
+export function authorizeUrl(config: OAuth2Config, state: string): string {
+	const params = new URLSearchParams({
+		response_type: 'code',
+		client_id: config.clientId,
+		redirect_uri: config.redirectUri,
+		scope: config.scope,
+		state,
+	});
+	return `${config.authorizeEndpoint}?${params.toString()}`;
+}
+
+export function base64EncodeString(str: string): string {
+	return Buffer.from(str).toString('base64');
+}

packages/oauth2/src/Token.tsx

@@ -0,0 +1,109 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type {OAuth2Config} from '@fluxer/oauth2/src/OAuth2';
+import {base64EncodeString} from '@fluxer/oauth2/src/OAuth2';
+
+export interface TokenResponse {
+	access_token: string;
+	token_type: string;
+	expires_in: number;
+	refresh_token?: string;
+	scope: string;
+}
+
+export interface LoggerInterface {
+	debug(obj: Record<string, unknown> | string, msg?: string): void;
+	info(obj: Record<string, unknown> | string, msg?: string): void;
+	warn(obj: Record<string, unknown> | string, msg?: string): void;
+	error(obj: Record<string, unknown> | string, msg?: string): void;
+}
+
+interface ExchangeCodeOptions {
+	logger?: LoggerInterface;
+}
+
+export async function exchangeCode(
+	config: OAuth2Config,
+	code: string,
+	options?: ExchangeCodeOptions,
+): Promise<TokenResponse | null> {
+	try {
+		const response = await fetch(config.tokenEndpoint, {
+			method: 'POST',
+			headers: {
+				'Content-Type': 'application/x-www-form-urlencoded',
+			},
+			body: new URLSearchParams({
+				grant_type: 'authorization_code',
+				code,
+				redirect_uri: config.redirectUri,
+				client_id: config.clientId,
+				client_secret: config.clientSecret,
+			}),
+		});
+
+		if (!response.ok) {
+			options?.logger?.warn(
+				{status: response.status, tokenEndpoint: config.tokenEndpoint},
+				'OAuth2 code exchange failed',
+			);
+			return null;
+		}
+
+		return (await response.json()) as TokenResponse;
+	} catch (err) {
+		options?.logger?.error(
+			{error: err instanceof Error ? err.message : String(err), tokenEndpoint: config.tokenEndpoint},
+			'OAuth2 code exchange error',
+		);
+		return null;
+	}
+}
+
+interface RevokeTokenOptions {
+	logger?: LoggerInterface;
+}
+
+export async function revokeToken(
+	config: OAuth2Config,
+	token: string,
+	revokeEndpoint: string,
+	options?: RevokeTokenOptions,
+): Promise<void> {
+	try {
+		const basic = `Basic ${base64EncodeString(`${config.clientId}:${config.clientSecret}`)}`;
+		await fetch(revokeEndpoint, {
+			method: 'POST',
+			headers: {
+				'Content-Type': 'application/x-www-form-urlencoded',
+				Authorization: basic,
+			},
+			body: new URLSearchParams({
+				token,
+				token_type_hint: 'access_token',
+			}),
+		});
+	} catch (err) {
+		options?.logger?.warn(
+			{error: err instanceof Error ? err.message : String(err), revokeEndpoint},
+			'OAuth2 token revocation failed',
+		);
+	}
+}

packages/oauth2/src/User.tsx

@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface UserInfo {
+	id: string;
+	username: string;
+	discriminator: number;
+	avatar: string | null;
+	email?: string;
+	acls?: Array<string>;
+}
+
+export interface LoggerInterface {
+	debug(obj: Record<string, unknown> | string, msg?: string): void;
+	info(obj: Record<string, unknown> | string, msg?: string): void;
+	warn(obj: Record<string, unknown> | string, msg?: string): void;
+	error(obj: Record<string, unknown> | string, msg?: string): void;
+}
+
+interface FetchUserOptions {
+	logger?: LoggerInterface;
+}
+
+export async function fetchUser(
+	apiEndpoint: string,
+	accessToken: string,
+	options?: FetchUserOptions,
+): Promise<UserInfo | null> {
+	try {
+		const response = await fetch(`${apiEndpoint}/users/@me`, {
+			headers: {
+				Authorization: `Bearer ${accessToken}`,
+			},
+		});
+
+		if (!response.ok) {
+			options?.logger?.warn({status: response.status, apiEndpoint}, 'OAuth2 user fetch failed');
+			return null;
+		}
+
+		return (await response.json()) as UserInfo;
+	} catch (err) {
+		options?.logger?.error(
+			{error: err instanceof Error ? err.message : String(err), apiEndpoint},
+			'OAuth2 user fetch error',
+		);
+		return null;
+	}
+}

packages/oauth2/src/__tests__/OAuth2.test.tsx

@@ -0,0 +1,163 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {authorizeUrl, base64EncodeString, generateState, type OAuth2Config} from '@fluxer/oauth2/src/OAuth2';
+import {describe, expect, it} from 'vitest';
+
+function createTestConfig(overrides?: Partial<OAuth2Config>): OAuth2Config {
+	return {
+		clientId: 'test-client-id',
+		clientSecret: 'test-client-secret',
+		redirectUri: 'https://example.com/callback',
+		authorizeEndpoint: 'https://auth.example.com/authorize',
+		tokenEndpoint: 'https://auth.example.com/token',
+		scope: 'openid profile email',
+		...overrides,
+	};
+}
+
+describe('generateState', () => {
+	it('should generate a base64url encoded string', () => {
+		const state = generateState();
+		expect(state).toMatch(/^[A-Za-z0-9_-]+$/);
+	});
+
+	it('should generate a string of appropriate length for 32 bytes', () => {
+		const state = generateState();
+		expect(state.length).toBe(43);
+	});
+
+	it('should generate unique states on each call', () => {
+		const state1 = generateState();
+		const state2 = generateState();
+		const state3 = generateState();
+		expect(state1).not.toBe(state2);
+		expect(state2).not.toBe(state3);
+		expect(state1).not.toBe(state3);
+	});
+
+	it('should not contain characters that need URL encoding', () => {
+		for (let i = 0; i < 10; i++) {
+			const state = generateState();
+			expect(state).not.toContain('+');
+			expect(state).not.toContain('/');
+			expect(state).not.toContain('=');
+		}
+	});
+});
+
+describe('authorizeUrl', () => {
+	it('should construct a valid authorization URL with all parameters', () => {
+		const config = createTestConfig();
+		const state = 'test-state-123';
+		const url = authorizeUrl(config, state);
+		const parsed = new URL(url);
+
+		expect(parsed.origin).toBe('https://auth.example.com');
+		expect(parsed.pathname).toBe('/authorize');
+		expect(parsed.searchParams.get('response_type')).toBe('code');
+		expect(parsed.searchParams.get('client_id')).toBe('test-client-id');
+		expect(parsed.searchParams.get('redirect_uri')).toBe('https://example.com/callback');
+		expect(parsed.searchParams.get('scope')).toBe('openid profile email');
+		expect(parsed.searchParams.get('state')).toBe('test-state-123');
+	});
+
+	it('should handle special characters in scope', () => {
+		const config = createTestConfig({scope: 'read:user write:repo'});
+		const state = 'test-state';
+		const url = authorizeUrl(config, state);
+		const parsed = new URL(url);
+
+		expect(parsed.searchParams.get('scope')).toBe('read:user write:repo');
+	});
+
+	it('should handle redirect URIs with query parameters', () => {
+		const config = createTestConfig({
+			redirectUri: 'https://example.com/callback?app=test',
+		});
+		const state = 'test-state';
+		const url = authorizeUrl(config, state);
+		const parsed = new URL(url);
+
+		expect(parsed.searchParams.get('redirect_uri')).toBe('https://example.com/callback?app=test');
+	});
+
+	it('should handle empty scope', () => {
+		const config = createTestConfig({scope: ''});
+		const state = 'test-state';
+		const url = authorizeUrl(config, state);
+		const parsed = new URL(url);
+
+		expect(parsed.searchParams.get('scope')).toBe('');
+	});
+
+	it('should handle authorize endpoint with existing query parameters', () => {
+		const config = createTestConfig({
+			authorizeEndpoint: 'https://auth.example.com/authorize?extra=param',
+		});
+		const state = 'test-state';
+		const url = authorizeUrl(config, state);
+
+		expect(url).toContain('authorize?extra=param?');
+		expect(url).toContain('response_type=code');
+	});
+
+	it('should properly encode special characters in state', () => {
+		const config = createTestConfig();
+		const state = 'state+with/special=chars';
+		const url = authorizeUrl(config, state);
+		const parsed = new URL(url);
+
+		expect(parsed.searchParams.get('state')).toBe('state+with/special=chars');
+	});
+});
+
+describe('base64EncodeString', () => {
+	it('should encode a simple string to base64', () => {
+		const encoded = base64EncodeString('hello');
+		expect(encoded).toBe('aGVsbG8=');
+	});
+
+	it('should encode credentials for Basic auth', () => {
+		const encoded = base64EncodeString('client_id:client_secret');
+		expect(encoded).toBe('Y2xpZW50X2lkOmNsaWVudF9zZWNyZXQ=');
+	});
+
+	it('should encode empty string', () => {
+		const encoded = base64EncodeString('');
+		expect(encoded).toBe('');
+	});
+
+	it('should encode unicode characters', () => {
+		const encoded = base64EncodeString('hello world');
+		expect(encoded).toBe('aGVsbG8gd29ybGQ=');
+	});
+
+	it('should encode special characters', () => {
+		const encoded = base64EncodeString('user:p@ss!word#123');
+		expect(encoded).toBe('dXNlcjpwQHNzIXdvcmQjMTIz');
+	});
+
+	it('should produce decodable output', () => {
+		const original = 'test-client:test-secret';
+		const encoded = base64EncodeString(original);
+		const decoded = Buffer.from(encoded, 'base64').toString();
+		expect(decoded).toBe(original);
+	});
+});

packages/oauth2/src/__tests__/Token.test.tsx

@@ -0,0 +1,335 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type {OAuth2Config} from '@fluxer/oauth2/src/OAuth2';
+import {exchangeCode, type LoggerInterface, revokeToken, type TokenResponse} from '@fluxer/oauth2/src/Token';
+import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
+
+function createTestConfig(overrides?: Partial<OAuth2Config>): OAuth2Config {
+	return {
+		clientId: 'test-client-id',
+		clientSecret: 'test-client-secret',
+		redirectUri: 'https://example.com/callback',
+		authorizeEndpoint: 'https://auth.example.com/authorize',
+		tokenEndpoint: 'https://auth.example.com/token',
+		scope: 'openid profile email',
+		...overrides,
+	};
+}
+
+function createTestTokenResponse(overrides?: Partial<TokenResponse>): TokenResponse {
+	return {
+		access_token: 'test-access-token',
+		token_type: 'Bearer',
+		expires_in: 3600,
+		refresh_token: 'test-refresh-token',
+		scope: 'openid profile email',
+		...overrides,
+	};
+}
+
+function createTestLogger(): LoggerInterface & {calls: Record<string, Array<unknown>>} {
+	const calls: Record<string, Array<unknown>> = {
+		debug: [],
+		info: [],
+		warn: [],
+		error: [],
+	};
+	return {
+		calls,
+		debug: (...args: Array<unknown>) => calls.debug.push(args),
+		info: (...args: Array<unknown>) => calls.info.push(args),
+		warn: (...args: Array<unknown>) => calls.warn.push(args),
+		error: (...args: Array<unknown>) => calls.error.push(args),
+	};
+}
+
+describe('exchangeCode', () => {
+	let originalFetch: typeof globalThis.fetch;
+
+	beforeEach(() => {
+		originalFetch = globalThis.fetch;
+	});
+
+	afterEach(() => {
+		globalThis.fetch = originalFetch;
+		vi.restoreAllMocks();
+	});
+
+	it('should exchange code for tokens successfully', async () => {
+		const config = createTestConfig();
+		const tokenResponse = createTestTokenResponse();
+
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: true,
+			json: () => Promise.resolve(tokenResponse),
+		});
+
+		const result = await exchangeCode(config, 'authorization-code');
+
+		expect(result).toEqual(tokenResponse);
+		expect(globalThis.fetch).toHaveBeenCalledWith(config.tokenEndpoint, {
+			method: 'POST',
+			headers: {
+				'Content-Type': 'application/x-www-form-urlencoded',
+			},
+			body: expect.any(URLSearchParams),
+		});
+	});
+
+	it('should send correct form data in request body', async () => {
+		const config = createTestConfig();
+		let capturedBody: URLSearchParams | undefined;
+
+		globalThis.fetch = vi.fn().mockImplementation((_url, options) => {
+			capturedBody = options?.body as URLSearchParams;
+			return Promise.resolve({
+				ok: true,
+				json: () => Promise.resolve(createTestTokenResponse()),
+			});
+		});
+
+		await exchangeCode(config, 'test-auth-code');
+
+		expect(capturedBody).toBeDefined();
+		expect(capturedBody?.get('grant_type')).toBe('authorization_code');
+		expect(capturedBody?.get('code')).toBe('test-auth-code');
+		expect(capturedBody?.get('redirect_uri')).toBe(config.redirectUri);
+		expect(capturedBody?.get('client_id')).toBe(config.clientId);
+		expect(capturedBody?.get('client_secret')).toBe(config.clientSecret);
+	});
+
+	it('should return null on non-ok response', async () => {
+		const config = createTestConfig();
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: false,
+			status: 400,
+		});
+
+		const result = await exchangeCode(config, 'invalid-code');
+
+		expect(result).toBeNull();
+	});
+
+	it('should log warning on non-ok response when logger provided', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: false,
+			status: 401,
+		});
+
+		await exchangeCode(config, 'invalid-code', {logger});
+
+		expect(logger.calls.warn.length).toBe(1);
+		expect(logger.calls.warn[0]).toEqual([
+			{status: 401, tokenEndpoint: config.tokenEndpoint},
+			'OAuth2 code exchange failed',
+		]);
+	});
+
+	it('should return null on network error', async () => {
+		const config = createTestConfig();
+		globalThis.fetch = vi.fn().mockRejectedValue(new Error('Network error'));
+
+		const result = await exchangeCode(config, 'auth-code');
+
+		expect(result).toBeNull();
+	});
+
+	it('should log error on fetch exception when logger provided', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+
+		globalThis.fetch = vi.fn().mockRejectedValue(new Error('Connection timeout'));
+
+		await exchangeCode(config, 'auth-code', {logger});
+
+		expect(logger.calls.error.length).toBe(1);
+		expect(logger.calls.error[0]).toEqual([
+			{error: 'Connection timeout', tokenEndpoint: config.tokenEndpoint},
+			'OAuth2 code exchange error',
+		]);
+	});
+
+	it('should handle non-Error exceptions', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+
+		globalThis.fetch = vi.fn().mockRejectedValue({code: 'ECONNREFUSED'});
+
+		await exchangeCode(config, 'auth-code', {logger});
+
+		expect(logger.calls.error.length).toBe(1);
+		expect(logger.calls.error[0]).toEqual([
+			{error: '[object Object]', tokenEndpoint: config.tokenEndpoint},
+			'OAuth2 code exchange error',
+		]);
+	});
+
+	it('should handle token response without refresh_token', async () => {
+		const config = createTestConfig();
+		const tokenResponse: TokenResponse = {
+			access_token: 'test-access-token',
+			token_type: 'Bearer',
+			expires_in: 3600,
+			scope: 'openid',
+		};
+
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: true,
+			json: () => Promise.resolve(tokenResponse),
+		});
+
+		const result = await exchangeCode(config, 'auth-code');
+
+		expect(result).toEqual(tokenResponse);
+		expect(result?.refresh_token).toBeUndefined();
+	});
+});
+
+describe('revokeToken', () => {
+	let originalFetch: typeof globalThis.fetch;
+
+	beforeEach(() => {
+		originalFetch = globalThis.fetch;
+	});
+
+	afterEach(() => {
+		globalThis.fetch = originalFetch;
+		vi.restoreAllMocks();
+	});
+
+	it('should revoke token with correct authorization header', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+		let capturedHeaders: Headers | Record<string, string> | undefined;
+
+		globalThis.fetch = vi.fn().mockImplementation((_url, options) => {
+			capturedHeaders = options?.headers;
+			return Promise.resolve({ok: true});
+		});
+
+		await revokeToken(config, 'token-to-revoke', revokeEndpoint);
+
+		expect(globalThis.fetch).toHaveBeenCalledWith(revokeEndpoint, expect.any(Object));
+		const authHeader = (capturedHeaders as Record<string, string>)?.Authorization;
+		expect(authHeader).toMatch(/^Basic /);
+
+		const base64Creds = authHeader?.replace('Basic ', '');
+		const decoded = Buffer.from(base64Creds ?? '', 'base64').toString();
+		expect(decoded).toBe(`${config.clientId}:${config.clientSecret}`);
+	});
+
+	it('should send correct form data in request body', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+		let capturedBody: URLSearchParams | undefined;
+
+		globalThis.fetch = vi.fn().mockImplementation((_url, options) => {
+			capturedBody = options?.body as URLSearchParams;
+			return Promise.resolve({ok: true});
+		});
+
+		await revokeToken(config, 'access-token-123', revokeEndpoint);
+
+		expect(capturedBody).toBeDefined();
+		expect(capturedBody?.get('token')).toBe('access-token-123');
+		expect(capturedBody?.get('token_type_hint')).toBe('access_token');
+	});
+
+	it('should use POST method with correct content type', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+		let capturedOptions: RequestInit | undefined;
+
+		globalThis.fetch = vi.fn().mockImplementation((_url, options) => {
+			capturedOptions = options;
+			return Promise.resolve({ok: true});
+		});
+
+		await revokeToken(config, 'token', revokeEndpoint);
+
+		expect(capturedOptions?.method).toBe('POST');
+		expect((capturedOptions?.headers as Record<string, string>)?.['Content-Type']).toBe(
+			'application/x-www-form-urlencoded',
+		);
+	});
+
+	it('should not throw on network error', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+
+		globalThis.fetch = vi.fn().mockRejectedValue(new Error('Network error'));
+
+		await expect(revokeToken(config, 'token', revokeEndpoint)).resolves.toBeUndefined();
+	});
+
+	it('should log warning on network error when logger provided', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+		const logger = createTestLogger();
+
+		globalThis.fetch = vi.fn().mockRejectedValue(new Error('Connection refused'));
+
+		await revokeToken(config, 'token', revokeEndpoint, {logger});
+
+		expect(logger.calls.warn.length).toBe(1);
+		expect(logger.calls.warn[0]).toEqual([
+			{error: 'Connection refused', revokeEndpoint},
+			'OAuth2 token revocation failed',
+		]);
+	});
+
+	it('should handle non-Error exceptions', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+		const logger = createTestLogger();
+
+		globalThis.fetch = vi.fn().mockRejectedValue('string error');
+
+		await revokeToken(config, 'token', revokeEndpoint, {logger});
+
+		expect(logger.calls.warn.length).toBe(1);
+		expect(logger.calls.warn[0]).toEqual([{error: 'string error', revokeEndpoint}, 'OAuth2 token revocation failed']);
+	});
+
+	it('should not log when revocation succeeds', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+		const logger = createTestLogger();
+
+		globalThis.fetch = vi.fn().mockResolvedValue({ok: true});
+
+		await revokeToken(config, 'token', revokeEndpoint, {logger});
+
+		expect(logger.calls.warn.length).toBe(0);
+		expect(logger.calls.error.length).toBe(0);
+	});
+
+	it('should work without logger option', async () => {
+		const config = createTestConfig();
+		const revokeEndpoint = 'https://auth.example.com/revoke';
+
+		globalThis.fetch = vi.fn().mockRejectedValue(new Error('Error'));
+
+		await expect(revokeToken(config, 'token', revokeEndpoint)).resolves.toBeUndefined();
+	});
+});

packages/oauth2/src/__tests__/User.test.tsx

@@ -0,0 +1,171 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {fetchUser, type LoggerInterface, type UserInfo} from '@fluxer/oauth2/src/User';
+import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
+
+const TEST_API_ENDPOINT = 'https://api.example.com';
+const TEST_ACCESS_TOKEN = 'test-access-token-123';
+
+function createTestUser(overrides?: Partial<UserInfo>): UserInfo {
+	return {
+		id: '123456789',
+		username: 'testuser',
+		discriminator: 1234,
+		avatar: 'abc123def456',
+		email: 'test@example.com',
+		acls: ['admin', 'moderator'],
+		...overrides,
+	};
+}
+
+function createTestLogger(): LoggerInterface & {calls: Record<string, Array<unknown>>} {
+	const calls: Record<string, Array<unknown>> = {
+		debug: [],
+		info: [],
+		warn: [],
+		error: [],
+	};
+	return {
+		calls,
+		debug: (...args: Array<unknown>) => calls.debug.push(args),
+		info: (...args: Array<unknown>) => calls.info.push(args),
+		warn: (...args: Array<unknown>) => calls.warn.push(args),
+		error: (...args: Array<unknown>) => calls.error.push(args),
+	};
+}
+
+describe('fetchUser', () => {
+	let originalFetch: typeof globalThis.fetch;
+
+	beforeEach(() => {
+		originalFetch = globalThis.fetch;
+	});
+
+	afterEach(() => {
+		globalThis.fetch = originalFetch;
+		vi.restoreAllMocks();
+	});
+
+	it('should fetch user info successfully', async () => {
+		const testUser = createTestUser();
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: true,
+			json: () => Promise.resolve(testUser),
+		});
+
+		const user = await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN);
+
+		expect(user).toEqual(testUser);
+		expect(globalThis.fetch).toHaveBeenCalledWith(`${TEST_API_ENDPOINT}/users/@me`, {
+			headers: {
+				Authorization: `Bearer ${TEST_ACCESS_TOKEN}`,
+			},
+		});
+	});
+
+	it('should return null on non-ok response', async () => {
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: false,
+			status: 401,
+		});
+
+		const user = await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN);
+
+		expect(user).toBeNull();
+	});
+
+	it('should log warning on non-ok response when logger provided', async () => {
+		const logger = createTestLogger();
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: false,
+			status: 403,
+		});
+
+		await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN, {logger});
+
+		expect(logger.calls.warn.length).toBe(1);
+		expect(logger.calls.warn[0]).toEqual([{status: 403, apiEndpoint: TEST_API_ENDPOINT}, 'OAuth2 user fetch failed']);
+	});
+
+	it('should return null on network error', async () => {
+		globalThis.fetch = vi.fn().mockRejectedValue(new Error('Network error'));
+
+		const user = await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN);
+
+		expect(user).toBeNull();
+	});
+
+	it('should log error on fetch exception when logger provided', async () => {
+		const logger = createTestLogger();
+		globalThis.fetch = vi.fn().mockRejectedValue(new Error('Connection refused'));
+
+		await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN, {logger});
+
+		expect(logger.calls.error.length).toBe(1);
+		expect(logger.calls.error[0]).toEqual([
+			{error: 'Connection refused', apiEndpoint: TEST_API_ENDPOINT},
+			'OAuth2 user fetch error',
+		]);
+	});
+
+	it('should handle non-Error exceptions', async () => {
+		const logger = createTestLogger();
+		globalThis.fetch = vi.fn().mockRejectedValue('string error');
+
+		await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN, {logger});
+
+		expect(logger.calls.error.length).toBe(1);
+		expect(logger.calls.error[0]).toEqual([
+			{error: 'string error', apiEndpoint: TEST_API_ENDPOINT},
+			'OAuth2 user fetch error',
+		]);
+	});
+
+	it('should fetch user without logger option', async () => {
+		const testUser = createTestUser();
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: true,
+			json: () => Promise.resolve(testUser),
+		});
+
+		const user = await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN);
+
+		expect(user).toEqual(testUser);
+	});
+
+	it('should handle user with minimal fields', async () => {
+		const minimalUser: UserInfo = {
+			id: '111',
+			username: 'minimal',
+			discriminator: 0,
+			avatar: null,
+		};
+		globalThis.fetch = vi.fn().mockResolvedValue({
+			ok: true,
+			json: () => Promise.resolve(minimalUser),
+		});
+
+		const user = await fetchUser(TEST_API_ENDPOINT, TEST_ACCESS_TOKEN);
+
+		expect(user).toEqual(minimalUser);
+		expect(user?.email).toBeUndefined();
+		expect(user?.acls).toBeUndefined();
+	});
+});

packages/oauth2/src/client/IOAuth2Client.tsx

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type {OAuth2TokenResponse} from '@fluxer/oauth2/src/models/OAuth2TokenResponse';
+import type {OAuth2UserInfo} from '@fluxer/oauth2/src/models/OAuth2UserInfo';
+
+export interface IOAuth2Client {
+	generateState(): string;
+	createAuthorizationUrl(state: string): string;
+	exchangeCodeForToken(code: string): Promise<OAuth2TokenResponse | null>;
+	fetchCurrentUser(accessToken: string): Promise<OAuth2UserInfo | null>;
+	revokeAccessToken(accessToken: string): Promise<void>;
+}

packages/oauth2/src/client/OAuth2Client.tsx

@@ -0,0 +1,163 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {randomBytes} from 'node:crypto';
+import type {IOAuth2Client} from '@fluxer/oauth2/src/client/IOAuth2Client';
+import type {OAuth2ClientConfig} from '@fluxer/oauth2/src/config/OAuth2ClientConfig';
+import {FetchHttpClient} from '@fluxer/oauth2/src/http/FetchHttpClient';
+import type {IOAuth2HttpClient} from '@fluxer/oauth2/src/http/IOAuth2HttpClient';
+import type {IOAuth2Logger} from '@fluxer/oauth2/src/logging/IOAuth2Logger';
+import type {OAuth2TokenResponse} from '@fluxer/oauth2/src/models/OAuth2TokenResponse';
+import type {OAuth2UserInfo} from '@fluxer/oauth2/src/models/OAuth2UserInfo';
+
+export interface OAuth2ClientDependencies {
+	httpClient?: IOAuth2HttpClient;
+	logger?: IOAuth2Logger;
+}
+
+export class OAuth2Client implements IOAuth2Client {
+	private readonly httpClient: IOAuth2HttpClient;
+	private readonly logger?: IOAuth2Logger;
+
+	constructor(
+		private readonly config: OAuth2ClientConfig,
+		dependencies?: OAuth2ClientDependencies,
+	) {
+		this.httpClient = dependencies?.httpClient ?? new FetchHttpClient();
+		this.logger = dependencies?.logger;
+	}
+
+	generateState(): string {
+		return randomBytes(32).toString('base64url');
+	}
+
+	createAuthorizationUrl(state: string): string {
+		const url = new URL(this.config.endpoints.authorizeEndpoint);
+		url.searchParams.set('response_type', 'code');
+		url.searchParams.set('client_id', this.config.clientId);
+		url.searchParams.set('redirect_uri', this.config.redirectUri);
+		url.searchParams.set('scope', this.config.scope);
+		url.searchParams.set('state', state);
+		return url.toString();
+	}
+
+	async exchangeCodeForToken(code: string): Promise<OAuth2TokenResponse | null> {
+		try {
+			const response = await this.httpClient.request(this.config.endpoints.tokenEndpoint, {
+				method: 'POST',
+				headers: {
+					'Content-Type': 'application/x-www-form-urlencoded',
+				},
+				body: new URLSearchParams({
+					grant_type: 'authorization_code',
+					code,
+					redirect_uri: this.config.redirectUri,
+					client_id: this.config.clientId,
+					client_secret: this.config.clientSecret,
+				}),
+			});
+
+			if (!response.ok) {
+				this.logger?.warn(
+					{status: response.status, tokenEndpoint: this.config.endpoints.tokenEndpoint},
+					'OAuth2 code exchange failed',
+				);
+				return null;
+			}
+
+			return (await response.json()) as OAuth2TokenResponse;
+		} catch (error) {
+			this.logger?.error(
+				{error: this.formatError(error), tokenEndpoint: this.config.endpoints.tokenEndpoint},
+				'OAuth2 code exchange error',
+			);
+			return null;
+		}
+	}
+
+	async fetchCurrentUser(accessToken: string): Promise<OAuth2UserInfo | null> {
+		try {
+			const response = await this.httpClient.request(this.config.endpoints.userInfoEndpoint, {
+				headers: {
+					Authorization: `Bearer ${accessToken}`,
+				},
+			});
+
+			if (!response.ok) {
+				this.logger?.warn(
+					{status: response.status, userInfoEndpoint: this.config.endpoints.userInfoEndpoint},
+					'OAuth2 user fetch failed',
+				);
+				return null;
+			}
+
+			return (await response.json()) as OAuth2UserInfo;
+		} catch (error) {
+			this.logger?.error(
+				{error: this.formatError(error), userInfoEndpoint: this.config.endpoints.userInfoEndpoint},
+				'OAuth2 user fetch error',
+			);
+			return null;
+		}
+	}
+
+	async revokeAccessToken(accessToken: string): Promise<void> {
+		try {
+			const response = await this.httpClient.request(this.config.endpoints.revokeEndpoint, {
+				method: 'POST',
+				headers: {
+					'Content-Type': 'application/x-www-form-urlencoded',
+					Authorization: this.createBasicAuthorizationHeader(),
+				},
+				body: new URLSearchParams({
+					token: accessToken,
+					token_type_hint: 'access_token',
+				}),
+			});
+
+			if (!response.ok) {
+				this.logger?.warn(
+					{status: response.status, revokeEndpoint: this.config.endpoints.revokeEndpoint},
+					'OAuth2 token revocation failed',
+				);
+			}
+		} catch (error) {
+			this.logger?.warn(
+				{error: this.formatError(error), revokeEndpoint: this.config.endpoints.revokeEndpoint},
+				'OAuth2 token revocation failed',
+			);
+		}
+	}
+
+	private createBasicAuthorizationHeader(): string {
+		const credentials = `${this.config.clientId}:${this.config.clientSecret}`;
+		return `Basic ${Buffer.from(credentials).toString('base64')}`;
+	}
+
+	private formatError(error: unknown): string {
+		if (error instanceof Error) {
+			return error.message;
+		}
+		return String(error);
+	}
+}
+
+export function createOAuth2Client(config: OAuth2ClientConfig, dependencies?: OAuth2ClientDependencies): IOAuth2Client {
+	return new OAuth2Client(config, dependencies);
+}

packages/oauth2/src/client/tests/OAuth2Client.test.tsx

@@ -0,0 +1,325 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {createOAuth2Client, OAuth2Client} from '@fluxer/oauth2/src/client/OAuth2Client';
+import type {OAuth2ClientConfig, OAuth2ClientEndpoints} from '@fluxer/oauth2/src/config/OAuth2ClientConfig';
+import type {IOAuth2HttpClient} from '@fluxer/oauth2/src/http/IOAuth2HttpClient';
+import type {IOAuth2Logger} from '@fluxer/oauth2/src/logging/IOAuth2Logger';
+import type {OAuth2TokenResponse} from '@fluxer/oauth2/src/models/OAuth2TokenResponse';
+import type {OAuth2UserInfo} from '@fluxer/oauth2/src/models/OAuth2UserInfo';
+import {describe, expect, it} from 'vitest';
+
+interface LoggerMethodCalls {
+	debug: Array<Array<unknown>>;
+	info: Array<Array<unknown>>;
+	warn: Array<Array<unknown>>;
+	error: Array<Array<unknown>>;
+}
+
+interface TestLogger extends IOAuth2Logger {
+	calls: LoggerMethodCalls;
+}
+
+interface OAuth2ClientConfigOverrides extends Partial<Omit<OAuth2ClientConfig, 'endpoints'>> {
+	endpoints?: Partial<OAuth2ClientEndpoints>;
+}
+
+interface RequestCall {
+	url: string;
+	init: RequestInit | undefined;
+}
+
+class TestHttpClient implements IOAuth2HttpClient {
+	public readonly calls: Array<RequestCall> = [];
+	private readonly queue: Array<unknown> = [];
+
+	enqueueResponse(response: Response): void {
+		this.queue.push(response);
+	}
+
+	enqueueError(error: unknown): void {
+		this.queue.push(error);
+	}
+
+	async request(url: string, init?: RequestInit): Promise<Response> {
+		this.calls.push({url, init});
+		const next = this.queue.shift();
+
+		if (next === undefined) {
+			throw new Error('TestHttpClient request queue is empty');
+		}
+
+		if (next instanceof Response) {
+			return next;
+		}
+
+		throw next;
+	}
+}
+
+function createTestConfig(overrides?: OAuth2ClientConfigOverrides): OAuth2ClientConfig {
+	const endpoints: OAuth2ClientEndpoints = {
+		authorizeEndpoint: overrides?.endpoints?.authorizeEndpoint ?? 'https://auth.example.com/authorize',
+		tokenEndpoint: overrides?.endpoints?.tokenEndpoint ?? 'https://auth.example.com/token',
+		userInfoEndpoint: overrides?.endpoints?.userInfoEndpoint ?? 'https://api.example.com/users/@me',
+		revokeEndpoint: overrides?.endpoints?.revokeEndpoint ?? 'https://auth.example.com/revoke',
+	};
+
+	return {
+		clientId: overrides?.clientId ?? 'test-client-id',
+		clientSecret: overrides?.clientSecret ?? 'test-client-secret',
+		redirectUri: overrides?.redirectUri ?? 'https://example.com/callback',
+		scope: overrides?.scope ?? 'identify email admin',
+		endpoints,
+	};
+}
+
+function createTestTokenResponse(overrides?: Partial<OAuth2TokenResponse>): OAuth2TokenResponse {
+	return {
+		access_token: 'test-access-token',
+		token_type: 'Bearer',
+		expires_in: 3600,
+		refresh_token: 'test-refresh-token',
+		scope: 'identify email admin',
+		...overrides,
+	};
+}
+
+function createTestUserInfo(overrides?: Partial<OAuth2UserInfo>): OAuth2UserInfo {
+	return {
+		id: '123456789',
+		username: 'test-user',
+		discriminator: 4242,
+		avatar: 'avatar-hash',
+		email: 'test@example.com',
+		acls: ['admin:authenticate'],
+		...overrides,
+	};
+}
+
+function createTestLogger(): TestLogger {
+	const calls: LoggerMethodCalls = {
+		debug: [],
+		info: [],
+		warn: [],
+		error: [],
+	};
+
+	return {
+		calls,
+		debug: (...args: Array<unknown>) => calls.debug.push(args),
+		info: (...args: Array<unknown>) => calls.info.push(args),
+		warn: (...args: Array<unknown>) => calls.warn.push(args),
+		error: (...args: Array<unknown>) => calls.error.push(args),
+	};
+}
+
+function getBodyAsSearchParams(init?: RequestInit): URLSearchParams {
+	if (init?.body instanceof URLSearchParams) {
+		return init.body;
+	}
+
+	throw new Error('Expected request body to be URLSearchParams');
+}
+
+function getAuthorizationHeader(init?: RequestInit): string | null {
+	const headers = new Headers(init?.headers);
+	return headers.get('Authorization');
+}
+
+describe('OAuth2Client', () => {
+	it('should create an OAuth2Client instance via the factory', () => {
+		const client = createOAuth2Client(createTestConfig());
+		expect(client).toBeInstanceOf(OAuth2Client);
+	});
+
+	it('should generate URL-safe state values with stable length', () => {
+		const client = createOAuth2Client(createTestConfig());
+		const firstState = client.generateState();
+		const secondState = client.generateState();
+
+		expect(firstState).toMatch(/^[A-Za-z0-9_-]+$/);
+		expect(firstState.length).toBe(43);
+		expect(firstState).not.toBe(secondState);
+	});
+
+	it('should build an authorization URL and preserve existing query params', () => {
+		const client = createOAuth2Client(
+			createTestConfig({
+				endpoints: {
+					authorizeEndpoint: 'https://auth.example.com/authorize?existing=value',
+				},
+			}),
+		);
+
+		const url = new URL(client.createAuthorizationUrl('state+with/special=chars'));
+
+		expect(url.origin).toBe('https://auth.example.com');
+		expect(url.pathname).toBe('/authorize');
+		expect(url.searchParams.get('existing')).toBe('value');
+		expect(url.searchParams.get('response_type')).toBe('code');
+		expect(url.searchParams.get('client_id')).toBe('test-client-id');
+		expect(url.searchParams.get('redirect_uri')).toBe('https://example.com/callback');
+		expect(url.searchParams.get('scope')).toBe('identify email admin');
+		expect(url.searchParams.get('state')).toBe('state+with/special=chars');
+	});
+
+	it('should exchange an authorization code for tokens', async () => {
+		const config = createTestConfig();
+		const tokenResponse = createTestTokenResponse();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueResponse(
+			new Response(JSON.stringify(tokenResponse), {
+				status: 200,
+				headers: {'Content-Type': 'application/json'},
+			}),
+		);
+
+		const client = createOAuth2Client(config, {httpClient});
+		const result = await client.exchangeCodeForToken('auth-code-123');
+
+		expect(result).toEqual(tokenResponse);
+		expect(httpClient.calls.length).toBe(1);
+		expect(httpClient.calls[0]?.url).toBe(config.endpoints.tokenEndpoint);
+		expect(httpClient.calls[0]?.init?.method).toBe('POST');
+
+		const body = getBodyAsSearchParams(httpClient.calls[0]?.init);
+		expect(body.get('grant_type')).toBe('authorization_code');
+		expect(body.get('code')).toBe('auth-code-123');
+		expect(body.get('redirect_uri')).toBe(config.redirectUri);
+		expect(body.get('client_id')).toBe(config.clientId);
+		expect(body.get('client_secret')).toBe(config.clientSecret);
+	});
+
+	it('should return null and log a warning when token exchange fails', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueResponse(new Response(null, {status: 401}));
+
+		const client = createOAuth2Client(config, {httpClient, logger});
+		const result = await client.exchangeCodeForToken('bad-code');
+
+		expect(result).toBeNull();
+		expect(logger.calls.warn).toEqual([
+			[{status: 401, tokenEndpoint: config.endpoints.tokenEndpoint}, 'OAuth2 code exchange failed'],
+		]);
+	});
+
+	it('should return null and log errors when token exchange throws', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueError(new Error('Network timeout'));
+
+		const client = createOAuth2Client(config, {httpClient, logger});
+		const result = await client.exchangeCodeForToken('auth-code');
+
+		expect(result).toBeNull();
+		expect(logger.calls.error).toEqual([
+			[{error: 'Network timeout', tokenEndpoint: config.endpoints.tokenEndpoint}, 'OAuth2 code exchange error'],
+		]);
+	});
+
+	it('should fetch the current user', async () => {
+		const config = createTestConfig();
+		const userInfo = createTestUserInfo();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueResponse(
+			new Response(JSON.stringify(userInfo), {
+				status: 200,
+				headers: {'Content-Type': 'application/json'},
+			}),
+		);
+
+		const client = createOAuth2Client(config, {httpClient});
+		const result = await client.fetchCurrentUser('test-access-token');
+
+		expect(result).toEqual(userInfo);
+		expect(httpClient.calls.length).toBe(1);
+		expect(httpClient.calls[0]?.url).toBe(config.endpoints.userInfoEndpoint);
+		expect(getAuthorizationHeader(httpClient.calls[0]?.init)).toBe('Bearer test-access-token');
+	});
+
+	it('should return null and log errors when user fetch throws', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueError('string error');
+
+		const client = createOAuth2Client(config, {httpClient, logger});
+		const result = await client.fetchCurrentUser('test-access-token');
+
+		expect(result).toBeNull();
+		expect(logger.calls.error).toEqual([
+			[{error: 'string error', userInfoEndpoint: config.endpoints.userInfoEndpoint}, 'OAuth2 user fetch error'],
+		]);
+	});
+
+	it('should revoke a token with basic auth credentials', async () => {
+		const config = createTestConfig();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueResponse(new Response(null, {status: 200}));
+
+		const client = createOAuth2Client(config, {httpClient});
+		await client.revokeAccessToken('token-to-revoke');
+
+		expect(httpClient.calls.length).toBe(1);
+		expect(httpClient.calls[0]?.url).toBe(config.endpoints.revokeEndpoint);
+		expect(httpClient.calls[0]?.init?.method).toBe('POST');
+
+		const authorizationHeader = getAuthorizationHeader(httpClient.calls[0]?.init);
+		expect(authorizationHeader).toMatch(/^Basic /);
+		const encodedCredentials = authorizationHeader?.replace('Basic ', '') ?? '';
+		const decodedCredentials = Buffer.from(encodedCredentials, 'base64').toString();
+		expect(decodedCredentials).toBe(`${config.clientId}:${config.clientSecret}`);
+
+		const body = getBodyAsSearchParams(httpClient.calls[0]?.init);
+		expect(body.get('token')).toBe('token-to-revoke');
+		expect(body.get('token_type_hint')).toBe('access_token');
+	});
+
+	it('should log warnings when revocation fails with non-ok status', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueResponse(new Response(null, {status: 500}));
+
+		const client = createOAuth2Client(config, {httpClient, logger});
+		await client.revokeAccessToken('token-to-revoke');
+
+		expect(logger.calls.warn).toEqual([
+			[{status: 500, revokeEndpoint: config.endpoints.revokeEndpoint}, 'OAuth2 token revocation failed'],
+		]);
+	});
+
+	it('should log warnings when revocation throws', async () => {
+		const config = createTestConfig();
+		const logger = createTestLogger();
+		const httpClient = new TestHttpClient();
+		httpClient.enqueueError(new Error('Connection reset'));
+
+		const client = createOAuth2Client(config, {httpClient, logger});
+		await client.revokeAccessToken('token-to-revoke');
+
+		expect(logger.calls.warn).toEqual([
+			[{error: 'Connection reset', revokeEndpoint: config.endpoints.revokeEndpoint}, 'OAuth2 token revocation failed'],
+		]);
+	});
+});

packages/oauth2/src/config/OAuth2ClientConfig.tsx

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface OAuth2ClientEndpoints {
+	authorizeEndpoint: string;
+	tokenEndpoint: string;
+	userInfoEndpoint: string;
+	revokeEndpoint: string;
+}
+
+export interface OAuth2ClientConfig {
+	clientId: string;
+	clientSecret: string;
+	redirectUri: string;
+	scope: string;
+	endpoints: OAuth2ClientEndpoints;
+}

packages/oauth2/src/http/FetchHttpClient.tsx

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type {IOAuth2HttpClient} from '@fluxer/oauth2/src/http/IOAuth2HttpClient';
+
+export class FetchHttpClient implements IOAuth2HttpClient {
+	async request(url: string, init?: RequestInit): Promise<Response> {
+		return fetch(url, init);
+	}
+}

packages/oauth2/src/http/IOAuth2HttpClient.tsx

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface IOAuth2HttpClient {
+	request(url: string, init?: RequestInit): Promise<Response>;
+}

packages/oauth2/src/logging/IOAuth2Logger.tsx

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface IOAuth2Logger {
+	debug(obj: Record<string, unknown> | string, msg?: string): void;
+	info(obj: Record<string, unknown> | string, msg?: string): void;
+	warn(obj: Record<string, unknown> | string, msg?: string): void;
+	error(obj: Record<string, unknown> | string, msg?: string): void;
+}

packages/oauth2/src/models/OAuth2TokenResponse.tsx

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface OAuth2TokenResponse {
+	access_token: string;
+	token_type: string;
+	expires_in: number;
+	refresh_token?: string;
+	scope: string;
+}

packages/oauth2/src/models/OAuth2UserInfo.tsx

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface OAuth2UserInfo {
+	id: string;
+	username: string;
+	discriminator: number;
+	avatar: string | null;
+	email?: string;
+	acls?: Array<string>;
+}

packages/oauth2/tsconfig.json

@@ -0,0 +1,5 @@
+{
+	"extends": "../../tsconfigs/package.json",
+	"compilerOptions": {},
+	"include": ["src/**/*"]
+}

packages/oauth2/vitest.config.ts

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import path from 'node:path';
+import {fileURLToPath} from 'node:url';
+import tsconfigPaths from 'vite-tsconfig-paths';
+import {defineConfig} from 'vitest/config';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+export default defineConfig({
+	plugins: [
+		tsconfigPaths({
+			root: path.resolve(__dirname, '../..'),
+		}),
+	],
+	test: {
+		globals: true,
+		environment: 'node',
+		include: ['**/*.{test,spec}.{ts,tsx}'],
+		exclude: ['node_modules', 'dist'],
+		coverage: {
+			provider: 'v8',
+			reporter: ['text', 'json', 'html'],
+			exclude: ['**/*.test.tsx', '**/*.spec.tsx', 'node_modules/'],
+		},
+	},
+});