swaf/src/components/CsrfProtectionComponent.ts

import ApplicationComponent from "../ApplicationComponent";
import {Request, Router} from "express";
import crypto from "crypto";
import {BadRequestError} from "../HttpError";

export default class CsrfProtectionComponent extends ApplicationComponent<void> {
    private static readonly excluders: ((req: Request) => boolean)[] = [];

    public static getCSRFToken(session: Express.Session): string {
        if (typeof session.csrf !== 'string') {
            session.csrf = crypto.randomBytes(64).toString('base64');
        }
        return session.csrf;
    }

    public static addExcluder(excluder: (req: Request) => boolean) {
        this.excluders.push(excluder);
    }

    public async handle(router: Router): Promise<void> {
        router.use(async (req, res, next) => {
            for (const excluder of CsrfProtectionComponent.excluders) {
                if (excluder(req)) return next();
            }

            if (!req.session) {
                throw new Error('Session is unavailable.');
            }

            res.locals.getCSRFToken = () => {
                return CsrfProtectionComponent.getCSRFToken(req.session!);
            };

            if (!['GET', 'HEAD', 'OPTIONS'].find(s => s === req.method)) {
                try {
                    if (!(await req.authGuard.isAuthenticatedViaRequest(req))) {
                        if (req.session.csrf === undefined) {
                            throw new InvalidCsrfTokenError(req.baseUrl, `You weren't assigned any CSRF token.`);
                        } else if (req.body.csrf === undefined) {
                            throw new InvalidCsrfTokenError(req.baseUrl, `You didn't provide any CSRF token.`);
                        } else if (req.session.csrf !== req.body.csrf) {
                            throw new InvalidCsrfTokenError(req.baseUrl, `Tokens don't match.`);
                        }
                    }
                } catch (e) {
                    next(e);
                    return;
                }
            }
            next();
        });
    }
}

class InvalidCsrfTokenError extends BadRequestError {
    constructor(url: string, details: string, cause?: Error) {
        super(
            `Invalid CSRF token`,
            `${details} We can't process this request. Please try again.`,
            url,
            cause
        );
    }

    get name(): string {
        return 'Invalid CSRF Token';
    }

    get errorCode(): number {
        return 401;
    }
}