Noah Petherbridge fb11295168 Re-sign JWT tokens for safer server deployments

2023-04-19 19:55:39 -07:00

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BareRTC

BareRTC is a simple WebRTC-based chat room application. It is especially designed to be plugged into any existing website, with or without a pre-existing base of users.

Live demo: BareRTC Demo Chat

It is very much in the style of the old-school Flash based webcam chat rooms of the early 2000's: a multi-user chat room with DMs and some users may broadcast video and others may watch multiple video feeds in an asynchronous manner. I thought that this should be such an obvious free and open source app that should exist, but it did not and so I had to write it myself.

Features
Configuration
Authentication
Moderator Commands
JSON APIs
Tour of the Codebase
Deploying This App
License

Features

Specify multiple Public Channels that all users have access to.
Users can open direct message (one-on-one) conversations with each other.
No long-term server side state: messages are pushed out as they come in.
Users may share pictures and GIFs from their computer, which are pushed out as data: URLs (images scaled and metadata stripped by server) directly to connected chatters with no storage required.
Users may broadcast their webcam which shows a camera icon by their name in the Who List. Users may click on those icons to open multiple camera feeds of other users they are interested in.
- Mutual webcam options: users may opt that anyone who views their cam must also be sharing their own camera first.
- Users may mark their own cameras as explicit/NSFW which marks the icon in red so other users can get a warning before clicking in (if NSFW is enabled in the settings.toml)
- Users may boot people off their camera, and to the booted person it appears the same as if the broadcaster had turned their camera off completely - the chat server lies about the camera status so the booted user can't easily tell they'd been booted.
Mobile friendly: works best on iPads and above but adapts to smaller screens well.
WebRTC means peer-to-peer video streaming so cheap on hosting costs!
Simple integration with your existing userbase via signed JWT tokens.
User configurable sound effects to be notified of DMs or users entering/exiting the room.

Some important features still lacking:

Operator commands
- /kick users
- /nsfw to mark someone's camera
- /ban users
- /op users (give temporary mod control)

Configuration

On first run it will create the default settings.toml file for you which you may then customize to your liking:

Version = 2
Title = "BareRTC"
Branding = "BareRTC"
WebsiteURL = "https://www.example.com"
CORSHosts = ["https://www.example.com"]
PermitNSFW = true
UseXForwardedFor = true
WebSocketReadLimit = 41943040
MaxImageWidth = 1280
PreviewImageWidth = 360

[JWT]
  Enabled = false
  Strict = true
  SecretKey = ""

[[PublicChannels]]
  ID = "lobby"
  Name = "Lobby"
  Icon = "fa fa-gavel"
  WelcomeMessages = ["Welcome to the chat server!", "Please follow the basic rules:\n\n1. Have fun\n2. Be kind"]

[[PublicChannels]]
  ID = "offtopic"
  Name = "Off Topic"
  WelcomeMessages = ["Welcome to the Off Topic channel!"]

A description of the config directives includes:

Website settings:
- Title goes in the title bar of the chat page.
- Branding is the title shown in the corner of the page. HTML is permitted here! You may write an <img> tag to embed an image or use custom markup to color and prettify your logo.
- WebsiteURL is the base URL of your actual website which is used in a couple of places:
  - The About page will link to your website.
  - If using JWT authentication, avatar and profile URLs may be relative (beginning with a "/") and will append to your website URL to safe space on the JWT token size!
- UseXForwardedFor: set it to true and (for logging) the user's remote IP will use the X-Real-IP header or the first address in X-Forwarded-For. Set this if you run the app behind a proxy like nginx if you want IPs not to be all localhost.
- CORSHosts: your website's domain names that will be allowed to access [JSON APIs](#JSON APIs), like /api/statistics.
- PermitNSFW: for user webcam streams, expressly permit "NSFW" content if the user opts in to mark their feed as such. Setting this will enable pop-up modals regarding NSFW video and give broadcasters an opt-in button, which will warn other users before they click in to watch.
- WebSocketReadLimit: sets a size limit for WebSocket messages - it essentially also caps the max upload size for shared images (add a buffer as images will be base64 encoded on upload).
- MaxImageWidth: for pictures shared in chat the server will resize them down to no larger than this width for the full size view.
- PreviewImageWidth: to not flood the chat, the image in chat is this wide and users can click it to see the MaxImageWidth in a lightbox modal.
JWT: settings for JWT Authentication.
- Enabled (bool): activate the JWT token authentication feature.
- Strict (bool): if true, only valid signed JWT tokens may log in. If false, users with no/invalid token can enter their own username without authentication.
- SecretKey (string): the JWT signing secret shared with your back-end app.
PublicChannels: list the public channels and their configuration. The default channel will be the first one listed.
- ID (string): an arbitrary 'username' for the chat channel, like "lobby".
- Name (string): the user friendly name for the channel, like "Off Topic"
- Icon (string, optional): CSS class names for FontAwesome icon for the channel, like "fa fa-message"
- WelcomeMessages ([]string, optional): messages that are delivered by ChatServer to the user when they connect to the server. Useful to give an introduction to each channel, list its rules, etc.

Authentication

BareRTC supports custom (user-defined) authentication with your app in the form of JSON Web Tokens (JWTs). JWTs will allow your existing app to handle authentication for users by signing a token that vouches for them, and the BareRTC app will trust your signed token.

The workflow is as follows:

Your existing app already has the user logged-in and you trust who they are. To get them into the chat room, your server signs a JWT token using a secret key that both it and BareRTC knows.
Your server redirects the user to your BareRTC website sending the JWT token as a jwt parameter, either in the query string (GET) or POST request.
- e.g. you send them to https://chat.example.com/?jwt=TOKEN
- If the JWT token is too long to fit in a query string, you may create a <form> with method="POST" that posts the jwt as a form field.
The BareRTC server will parse and validate the token using the shared Secret Key that only it and your back-end website knows.

There are JWT libraries available for most programming languages.

Configure a shared secret key (random text string) in both the BareRTC settings and in your app, and your app will sign a JWT including claims that look like the following (using signing method HS264):

// JSON Web Token "claims" expected by BareRTC
{
    // Custom claims
    "sub": "username", // Username for chat (standard JWT claim)
    "op": true,  // User will have admin/operator permissions.
    "img": "/static/photos/username.jpg", // user picture URL
    "url": "/u/username",                 // user profile URL

    // Standard JWT claims that we support:
    "iss": "my own app", // Issuer name
    "exp": 1675645084,   // Expires at (time): 5 minutes out is plenty!
    "nbf": 1675644784,   // Not Before (time)
    "iat": 1675644784,   // Issued At (time)
}

Notice: your picture and profile URL may be relative URIs beginning with a forward slash as seen above; BareRTC will append them to the end of your WebsiteURL and you can save space on your JWT token size this way. Full URLs beginning with https?:// will also be accepted and used as-is.

An example how to sign your JWT tokens in Go (using golang-jwt):

import "github.com/golang-jwt/jwt/v4"

// JWT signing key - keep it a secret on your back-end shared between
// your app and BareRTC, do not use it in front-end javascript code or
// where a user can find it.
const SECRET = "change me"

// Your custom JWT claims.
type CustomClaims struct {
    // Custom claims used by BareRTC.
    Avatar     string `json:"img"`  // URI to user profile picture
    ProfileURL string `json:"url"`  // URI to user's profile page
    IsAdmin    bool   `json:"op"`   // give operator permission

    // Standard JWT claims
    jwt.RegisteredClaims
}

// Assuming your internal User struct looks anything at all like:
type User struct {
    Username       string
    IsAdmin        bool
    ProfilePicture string  // like "/static/photos/username.jpg"
}

// Create a JWT token for this user.
func SignForUser(user User) string {
    claims := CustomClaims{
        // Custom claims
        ProfileURL: "/users/" + user.Username,
        Avatar:     user.ProfilePicture,
        IsAdmin:    user.IsAdmin,

        // Standard claims
        Subject:   user.Username, // their chat username!
        ExpiresAt: time.Now().Add(5 * time.Minute),
        IssuedAt:  time.Now(),
        NotBefore: time.Now(),
        Issuer:    "my own app",
        ID:        user.ID,
    }
    token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
    tokenStr, err := token.SignedString(SECRET)
    if err != nil {
        panic(err)
    }
    return tokenstr
}

JWT Strict Mode

You can enable JWT authentication in a mixed mode: users presenting a valid token will get a profile picture and operator status (if applicable) and users who don't have a JWT token are asked to pick their own username and don't get any special flair.

In strict mode (default/recommended), only a valid JWT token can sign a user into the chat room. Set [JWT]/Strict=false in your settings.toml to disable strict JWT verification and allow "guest users" to log in. Note that this can have the same caveats as running without authentication and is not a recommended use case.

Running Without Authentication

The default app doesn't need any authentication at all: users are asked to pick their own username when joining the chat. The server may re-assign them a new name if they enter one that's already taken.

It is not recommended to run in this mode as admin controls to moderate the server are disabled.

Known Bugs Running Without Authentication

This app is not designed to run without JWT authentication for users enabled. In the app's default state, users can pick their own username when they connect and the server will adjust their name to resolve duplicates. Direct message threads are based on the username so if a user logs off, somebody else could log in with the same username and "resume" direct message threads that others were involved in.

Note that they would not get past history of those DMs as this server only pushes new messages to users after they connect.

Moderator Commands

If you authenticate an Op user via JWT they can enter IRC-style chat commands to moderate the server. Current commands include:

/kick <username> to disconnect a user's chat session.
/nsfw <username> to tag a user's video feed as NSFW (if your settings.toml has PermitNSFW enabled).

JSON APIs

For better integration with your website, the chat server exposes some data via JSON APIs ready for cross-origin ajax requests. In your settings.toml set the CORSHosts to your list of website domains, such as "https://www.example.com", "http://localhost:8080" or so on.

Current API endpoints include:

GET /api/statistics

Returns basic info about the count and usernames of connected chatters:

{
    "UserCount": 1,
    "Usernames": ["admin"]
}

Tour of the Codebase

This app uses WebSockets and WebRTC at the very simplest levels, without using a framework like Socket.io. Here is a tour of the codebase with the more interesting modules listed first.

Backend files

cmd/BareRTC/main.go: the entry point for the Go back-end application (parses command-line flags and starts the web server)
pkg/ contains the Go source code for the server side (the application).
- config/ handles the settings.toml config file for the app.
- jwt/ handles the JWT authentication logic
- log/ is an internal logger library - not very interesting
- util/ houses some miscellaneous utility functions, such as generating random strings or getting the user's IP address (w/ X-Forwarded-For support, etc.)
pkg/server.go sets up the Go HTTP server and all the endpoint routes (e.g.: the /about page, static files, the WebSockets endpoint)
pkg/websocket.go handles the WebSockets endpoint which drives 99% of the chat app (all the login, text chat, who list portions - not webcams). Some related files to this include:
- pkg/messages.go is where I define the JSON message schema for the WebSockets protocol. Client and server messages marshal into the Message struct.
- pkg/handlers.go is where I write "high level" chat event handlers (OnLogin, OnMessage, etc.) - the WebSocket read loop parses their message and then nicely calls my event handler based on action.
- pkg/commands.go handles commands like /kick from moderators.
pkg/api.go handles the JSON API endpoints from the web server.
pkg/pages.go handles the index (w/ jwt parsing) and about pages.

Frontend files

The web/ folder holds front-end files and templates used by the Go app.

web/templates holds Go html/template sources that are rendered server-side.
- chat.html is the template for the main chat page (index route, /).
- about.html is the template for the /about page.
web/static holds the static files (scripts, stylesheets, images) for the site.
- js/BareRTC.js does the whole front-end Vue.js app for BareRTC. The portions of the code that handle the WebSockets and WebRTC features are marked off with comment banners so you can scroll until you find them.
- js/sounds.js handles the sound effects for the chat room.
- css/chat.css has custom CSS for the chat room UI (mainly a lot of CSS Grid stuff for the full-screen layout).

Other front-end files are all vendored libraries or frameworks used by this app:

Bulma CSS framework
Font Awesome for icons.

Deploying This App

It is recommended to use a reverse proxy such as nginx in front of this app. You will need to configure nginx to forward WebSocket related headers:

server {
    server_name chat.example.com;
    listen 443 ssl http2;
    listen [::]:443 ssl http2;

    ssl_certificate /etc/letsencrypt/live/chat.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/chat.example.com/privkey.pem;

    # Proxy pass to BareRTC.
    location / {
        proxy_pass http://127.0.0.1:9000;

        # WebSocket headers to forward along.
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_set_header Host $host;
    }
}

You can run the BareRTC app itself using any service supervisor you like. I use Supervisor and you can configure BareRTC like so:

# /etc/supervisor/conf.d/barertc.conf
[program:barertc]
command = /home/user/git/BareRTC/BareRTC -address 127.0.0.1:9000
directory = /home/user/git/BareRTC
user = user

Then sudo supervisorctl reread && sudo supervisorctl add barertc to start the app.

License

GPLv3.

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