Implement register and login with Telegram

Add the concept of authentication methods that authenticate an account
where using the telegram login widget is one such method.  If a login is
done with an authentication method that's not associated with any
account the session ends up with the data from the authentication
method in order to allow registering a new account with the
authentication method.

This has to be stored on the session as otherwise it wouldn't be
possible to implement authentication methods such as OAuth2 that takes
the user to a third-party site and then redirects the browser back.

server/api/auth/account.post.ts

@@ -2,20 +2,21 @@
 	SPDX-FileCopyrightText: © 2025 Hornwitser <code@hornwitser.no>
 	SPDX-License-Identifier: AGPL-3.0-or-later
 */
-import { readUsers, writeUsers, nextUserId, type ServerUser } from "~/server/database";
+import { readUsers, writeUsers, nextUserId, type ServerUser, readAuthenticationMethods, nextAuthenticationMethodId, writeAuthenticationMethods } from "~/server/database";
 import { broadcastEvent } from "~/server/streams";
+import { ApiSession } from "~/shared/types/api";
 
-export default defineEventHandler(async (event) => {
+export default defineEventHandler(async (event): Promise<ApiSession> => {
 	let session = await getServerSession(event, false);
-	if (session) {
+	if (session?.accountId !== undefined) {
 		throw createError({
 			status: 409,
-			message: "Cannot create account while having an active session."
+			message: "Cannot create account while logged in to an account."
 		});
 	}
 
-	const formData = await readFormData(event);
-	const name = formData.get("name");
+	const formData = await readBody(event);
+	const name = formData.name;
 
 	const users = await readUsers();
 	let user: ServerUser;
@@ -54,11 +55,35 @@ export default defineEventHandler(async (event) => {
 		});
 	}
 
+	if (session?.authenticationProvider) {
+		const authMethods = await readAuthenticationMethods();
+		const method = authMethods.find(method => (
+			method.provider === session.authenticationProvider
+			&& method.slug === session.authenticationSlug
+		));
+		if (method) {
+			throw createError({
+				statusCode: 409,
+				statusMessage: "Conflict",
+				message: "A user is already associated with the authentication method",
+			});
+		}
+		authMethods.push({
+			id: await nextAuthenticationMethodId(),
+			userId: user.id,
+			provider: session.authenticationProvider,
+			slug: session.authenticationSlug!,
+			name: session.authenticationName!,
+		})
+		await writeAuthenticationMethods(authMethods);
+	}
+
 	users.push(user);
 	await writeUsers(users);
 	await broadcastEvent({
 		type: "user-update",
 		data: user,
 	});
-	await setServerSession(event, user);
+	const newSession = await setServerSession(event, user);
+	return await serverSessionToApi(event, newSession);
 })

server/api/auth/ap/telegram-login.post.ts

@@ -0,0 +1,100 @@
+/*
+	SPDX-FileCopyrightText: © 2025 Hornwitser <code@hornwitser.no>
+	SPDX-License-Identifier: AGPL-3.0-or-later
+*/
+import * as fs from "node:fs/promises";
+import type { H3Event } from "h3";
+import { string, z } from "zod/v4-mini";
+import { readAuthenticationMethods, readUsers } from "~/server/database";
+import { type TelegramAuthData, telegramAuthDataSchema } from "~/shared/types/telegram";
+import { ApiSession } from "~/shared/types/api";
+
+const loginSchema = z.object({
+	authData: telegramAuthDataSchema,
+});
+
+let cachedTelegramConfig:
+	| undefined
+	| { enabled: false }
+	| { enabled: true, botUsername: string, secretKey: CryptoKey }
+;
+async function useTelegramConfig(event: H3Event) {
+	if (cachedTelegramConfig)
+		return cachedTelegramConfig;
+
+	const runtimeConfig = useRuntimeConfig(event);
+	if (!runtimeConfig.public.authTelegramEnabled) {
+		return cachedTelegramConfig = {
+			enabled: false,
+		};
+	}
+	if (!runtimeConfig.telegramBotTokenFile) throw new Error("NUXT_TELEGRAM_BOT_TOKEN_FILE not configured");
+	if (!runtimeConfig.public.telegramBotUsername) throw new Error("NUXT_PUBLIC_TELEGRAM_BOT_USERNAME not configured");
+
+	const botToken = await fs.readFile(runtimeConfig.telegramBotTokenFile);
+	const secretKey = await crypto.subtle.importKey(
+		"raw",
+		await crypto.subtle.digest("SHA-256", botToken),
+		{
+			name: "HMAC",
+			hash: "SHA-256",
+		},
+		false,
+		["verify"],
+	);
+	return cachedTelegramConfig = {
+		enabled: true,
+		botUsername: runtimeConfig.public.telegramBotUsername,
+		secretKey,
+	}
+}
+
+async function validateTelegramAuthData(authData: TelegramAuthData, key: CryptoKey) {
+	const { hash, ...checkData } = authData;
+	const checkString = Object.entries(checkData).map(([key, value]) => `${key}=${value}`).sort().join("\n");
+	const signature = Buffer.from(hash, "hex");
+	return await crypto.subtle.verify("HMAC", key, signature, Buffer.from(checkString));
+}
+
+export default defineEventHandler(async (event): Promise<ApiSession> => {
+	const { success, error, data } = loginSchema.safeParse(await readBody(event));
+	if (!success) {
+		throw createError({
+			statusCode: 400,
+			statusMessage: "Bad Request",
+			message: z.prettifyError(error),
+		});
+	}
+
+	const config = await useTelegramConfig(event);
+	if (!config.enabled) {
+		throw createError({
+			statusCode: 403,
+			statusMessage: "Forbidden",
+			message: "Telegram authentication is disabled",
+		});
+	}
+
+	if (!await validateTelegramAuthData(data.authData, config.secretKey)) {
+		throw createError({
+			statusCode: 403,
+			statusMessage: "Forbidden",
+			message: "Validating authentication data failed",
+		});
+	}
+
+	const slug = String(data.authData.id);
+	const authMethods = await readAuthenticationMethods();
+	const method = authMethods.find(method => method.provider === "telegram" && method.slug === slug);
+	let session;
+	if (method) {
+		const users = await readUsers();
+		const account = users.find(user => !user.deleted && user.id === method.userId);
+		session = await setServerSession(event, account);
+	} else {
+		const name = data.authData.username ? "@" + data.authData.username : slug;
+		session = await setServerSession(event, undefined, "telegram", slug, name);
+	}
+
+	return await serverSessionToApi(event, session);
+})

server/database.ts

@@ -10,6 +10,9 @@ export interface ServerSession {
 	id: Id,
 	access: ApiUserType,
 	accountId?: number,
+	authenticationProvider?: "telegram",
+	authenticationSlug?: string,
+	authenticationName?: string,
 	rotatesAtMs: number,
 	expiresAtMs?: number,
 	discardAtMs: number,
@@ -28,6 +31,14 @@ export interface ServerUser {
 	locale?: string,
 }
 
+export interface ServerAuthenticationMethod {
+	id: Id,
+	provider: "telegram",
+	slug: string,
+	name: string,
+	userId: Id,
+}
+
 // For this demo I'm just storing the runtime data in JSON files. When making
 // this into proper application this should be replaced with an actual database.
 
@@ -37,6 +48,8 @@ const usersPath = "data/users.json";
 const nextUserIdPath = "data/next-user-id.json";
 const sessionsPath = "data/sessions.json";
 const nextSessionIdPath = "data/next-session-id.json";
+const authMethodPath = "data/auth-method.json";
+const nextAuthenticationMethodIdPath = "data/auth-method-id.json"
 
 async function remove(path: string) {
 	try {
@@ -137,3 +150,17 @@ export async function readSessions() {
 export async function writeSessions(sessions: ServerSession[]) {
 	await writeFile(sessionsPath, JSON.stringify(sessions, undefined, "\t") + "\n", "utf-8");
 }
+
+export async function nextAuthenticationMethodId() {
+	const nextId = await readJson(nextAuthenticationMethodIdPath, 0);
+	await writeFile(nextAuthenticationMethodIdPath, String(nextId + 1), "utf-8");
+	return nextId;
+}
+
+export async function readAuthenticationMethods() {
+	return readJson<ServerAuthenticationMethod[]>(authMethodPath, [])
+}
+
+export async function writeAuthenticationMethods(authMethods: ServerAuthenticationMethod[]) {
+	await writeFile(authMethodPath, JSON.stringify(authMethods, undefined, "\t") + "\n", "utf-8");
+}

server/utils/session.ts

@@ -51,7 +51,13 @@ export async function clearServerSession(event: H3Event) {
 	deleteCookie(event, "session");
 }
 
-export async function setServerSession(event: H3Event, account: ServerUser) {
+export async function setServerSession(
+	event: H3Event,
+	account: ServerUser | undefined,
+	authenticationProvider?: "telegram",
+	authenticationSlug?: string,
+	authenticationName?: string,
+) {
 	const sessions = await readSessions();
 	const runtimeConfig = useRuntimeConfig(event);
 	await clearServerSessionInternal(event, sessions);
@@ -60,6 +66,9 @@ export async function setServerSession(event: H3Event, account: ServerUser) {
 	const newSession: ServerSession = {
 		access: account?.type ?? "anonymous",
 		accountId: account?.id,
+		authenticationProvider,
+		authenticationSlug,
+		authenticationName,
 		rotatesAtMs: now + runtimeConfig.sessionRotatesTimeout * 1000,
 		discardAtMs: now + runtimeConfig.sessionDiscardTimeout * 1000,
 		id: await nextSessionId(),
@@ -68,6 +77,7 @@ export async function setServerSession(event: H3Event, account: ServerUser) {
 	sessions.push(newSession);
 	await writeSessions(sessions);
 	await setSignedCookie(event, "session", String(newSession.id), runtimeConfig.sessionDiscardTimeout)
+	return newSession;
 }
 
 async function rotateSession(event: H3Event, sessions: ServerSession[], session: ServerSession) {
@@ -78,6 +88,7 @@ async function rotateSession(event: H3Event, sessions: ServerSession[], session:
 	const newSession: ServerSession = {
 		accountId: account?.id,
 		access: account?.type ?? "anonymous",
+		// Authentication provider is removed to avoid possibility of an infinite delay before using it.
 		rotatesAtMs: now + runtimeConfig.sessionRotatesTimeout * 1000,
 		discardAtMs: now + runtimeConfig.sessionDiscardTimeout * 1000,
 		id: await nextSessionId(),
@@ -172,6 +183,8 @@ export async function serverSessionToApi(event: H3Event, session: ServerSession)
 	return {
 		id: session.id,
 		account,
+		authenticationProvider: session.authenticationProvider,
+		authenticationName: session.authenticationName,
 		push,
 	};
 }