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109 lines
4.7 KiB
109 lines
4.7 KiB
/**
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* Endpoint to support DiscourseConnect, to allow users to use their Grist logins for the
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* Grist Community Forum.
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*
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* Adds one endpoint:
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* - /discourse-connect: sends signed user info in a redirect to DISCOURSE_SITE.
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*
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* Expects environment variables:
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* - DISCOURSE_SITE: URL of the Discourse site to which to redirect back.
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* - DISCOURSE_CONNECT_SECRET: Secret for checking and adding signatures.
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*
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* This follows documentation at
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* https://meta.discourse.org/t/discourseconnect-official-single-sign-on-for-discourse-sso/13045
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* The recommended Discourse configuration includes:
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* - enable discourse connect: true
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* - discourse connect url: GRIST_SITE/discourse-connect
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* - discourse connect secret: DISCOURSE_CONNECT_SECRET
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* - logout redirect (in Users): GRIST_SITE/logout?next=DISCOURSE_SITE
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*/
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import type {Express, NextFunction, Request, RequestHandler, Response} from 'express';
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import type {RequestWithLogin} from 'app/server/lib/Authorizer';
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import {expressWrap} from 'app/server/lib/expressWrap';
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import {getOriginUrl} from 'app/server/lib/requestUtils';
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import * as crypto from 'crypto';
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const DISCOURSE_CONNECT_SECRET = process.env.DISCOURSE_CONNECT_SECRET;
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const DISCOURSE_SITE = process.env.DISCOURSE_SITE;
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// A hook for dependency injection. Allows tests to override these variables on the fly.
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export const Deps = {DISCOURSE_CONNECT_SECRET, DISCOURSE_SITE};
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// Calculate payload signature using the given secret.
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export function calcSignature(payload: string, secret: string) {
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return crypto.createHmac('sha256', secret).update(payload).digest('hex');
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}
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// Check configuration and signature of the Discourse nonce in the request.
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function checkParams(req: Request, resp: Response, next: NextFunction) {
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if (!Deps.DISCOURSE_SITE || !Deps.DISCOURSE_CONNECT_SECRET) {
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throw new Error('DiscourseConnect not configured');
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}
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const payload = String(req.query.sso || '');
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const signature = String(req.query.sig || '');
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if (calcSignature(payload, Deps.DISCOURSE_CONNECT_SECRET) !== signature) {
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throw new Error('Invalid signature for Discourse SSO request');
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}
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const params = new URLSearchParams(Buffer.from(payload, 'base64').toString('utf8'));
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const nonce = params.get('nonce');
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if (!nonce) {
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throw new Error('Invalid request for Discourse SSO');
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}
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(req as any).discourseConnectNonce = nonce;
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next();
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}
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// Respond to the DiscourseConnect request by redirecting back to discourse, including the user
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// info and a signature into the URL parameters.
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function discourseConnect(req: Request, resp: Response) {
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const mreq = req as RequestWithLogin;
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const nonce: string|undefined = (req as any).discourseConnectNonce;
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if (!nonce) {
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throw new Error('Invalid request for Discourse SSO');
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}
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if (!mreq.userIsAuthorized || !mreq.user?.loginEmail) {
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throw new Error('User is not authenticated');
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}
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if (!req.query.user && mreq.users && mreq.users.length > 1) {
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const origUrl = new URL(req.originalUrl, getOriginUrl(req));
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const redirectUrl = new URL('/welcome/select-account', getOriginUrl(req));
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redirectUrl.searchParams.set('next', origUrl.toString());
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return resp.redirect(redirectUrl.toString());
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}
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const responseObj: {[key: string]: string} = {
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nonce,
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email: mreq.user.loginEmail,
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// We don't treat user IDs as secret, so use the same ID with Discourse directly.
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external_id: String(mreq.user.id),
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// We could specify the username (used for @ mentions), but let Discourse create one for us
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// (it bases it on name or email). The user can change it within Discourse.
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// username,
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name: mreq.user.name,
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...(mreq.user.picture ? {avatar_url: mreq.user.picture} : {}),
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suppress_welcome_message: 'true',
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};
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const responseString = new URLSearchParams(responseObj).toString();
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const responsePayload = Buffer.from(responseString, 'utf8').toString('base64');
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const responseSignature = calcSignature(responsePayload, Deps.DISCOURSE_CONNECT_SECRET!);
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const redirectUrl = new URL('/session/sso_login', Deps.DISCOURSE_SITE);
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redirectUrl.search = new URLSearchParams({sso: responsePayload, sig: responseSignature}).toString();
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return resp.redirect(redirectUrl.toString());
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}
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/**
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* Attach the endpoint for /discourse-connect, as documented at
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* https://meta.discourse.org/t/discourseconnect-official-single-sign-on-for-discourse-sso/13045
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*/
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export function addDiscourseConnectEndpoints(app: Express, options: {
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userIdMiddleware: RequestHandler,
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redirectToLogin: RequestHandler,
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}) {
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app.get('/discourse-connect',
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expressWrap(checkParams), // Check early, to fail early if Discourse is misconfigured.
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options.userIdMiddleware,
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options.redirectToLogin,
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expressWrap(discourseConnect)
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);
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}
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