websites/packages/auth/providers/telegram.ts

import { AuthDataValidator } from '@telegram-auth/server';
import { objectToAuthDataMap } from '@telegram-auth/server/utils';
import type { Session } from 'next-auth';
import type { JWT } from 'next-auth/jwt';
import CredentialsProvider from 'next-auth/providers/credentials';

type TelegramProviderOptions = {
  botToken: string;
};

/**
 * TelegramProvider is a provider for authenticating users using Telegram.
 *
 * @param botToken - The Telegram bot token.
 * @returns A credentials provider for Telegram authentication.
 */
export const TelegramProvider = ({ botToken }: TelegramProviderOptions) =>
  CredentialsProvider({
    id: 'telegram',
    name: 'Telegram',
    credentials: {},
    /** @ts-expect-error -- trust me im right -- we are enforcing the return to include the telegram id */
    async authorize(_credentials, req) {
      const validator = new AuthDataValidator({ botToken });

      const data = objectToAuthDataMap(req.query || {});

      const user = await validator.validate(data);

      return {
        id: user.id,
        name: user.first_name,
        username: user.username,
      };
    },
  });

/**
 * Handles the Telegram session by updating the session object with the Telegram user ID. This is necessary because NextAuth does not properly return the user ID.
 *
 * @param options The options for handling the Telegram session.
 * @param options.session The session object.
 * @param options.token The JWT token.
 * @returns The updated session object.
 *
 * @example
 * ```ts
 * callbacks: {
      async session({ session, token }) {
        handleTelegramSession({ session, token });
        return session;
      },
    },
 * ```
 */
export function handleTelegramSession({ session, token }: { session: Session; token: JWT }) {
  if (token.sub) {
    if (!token?.picture?.includes('discord')) {
      // @ts-expect-error -- Next auth doesnt properly return the user id, this fixes that
      session.user.telegramId = token.sub;
    }
  }
}