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IRC × OAuth 2.0

In the past few days I’ve been working on better integrating IRC with OAuth 2.0. In a nutshell, my goal is to make IRC clients obtain a token by interacting with an OAuth 2.0 server, and then use that token to authenticate with the IRC server. This effort has resulted in various patches for meta.sr.ht’s OAuth 2.0 server, for the soju IRC bouncer and for the gamja & goguma IRC clients.

Motivation

My motivation is to improve chat.sr.ht’s authentication. chat.sr.ht is a hosted soju IRC bouncer for SourceHut users. The soju instance delegates authentication to meta.sr.ht so that users can login with their SourceHut credentials.

The status quo is not ideal:

  • When connecting from an IRC client, users need to jump through hoops. They need to manually generate a personal access token and copy/paste it into the password field. This is especially annoying on mobile. Wouldn’t it be nice to just click a button, fill the SourceHut login form that gets presented to you, and poof everything Just Works™?
  • We maintain a soju fork (in the srht branch) with special patches to integrate with SourceHut. It’s not the end of the world, but rebasing is never fun and error-prone, and it would be much nicer to be able to use vanilla soju.
  • The access tokens expire after 1 year. When that happens, users are greeted with an error message and need to manually generate a new personal access token again. It would be nicer to automatically refresh the token if possible, and show up a login form if not. Similarly, it would be nice to revoke access tokens when a user logs out explicitly, instead of leaving behind unused tokens.

I’d like the solution to these problems to only use standardized APIs. That way any client or server with similar needs can implement the same standards and inter-operate with each other. For instance, one could add support for the standards in a GTK IRC client and have it work with chat.sr.ht. One could setup soju to use a GitLab instance as an OAuth server for authentication.

Before anybody complains about OAuth ruining IRC: this effort is just adding new optional things clients can add support for if they want to. I expect OAuth to be out-of-scope for many IRC clients and that’s perfectly fine. The current approach of passing a personal access token as the password will keep working.

Here is a video of the end result: user loads gamja, is asked confirmation by SourceHut, then is redirected back straight to a ready-to-use gamja. The experience on Goguma is similar.

High-level overview

┌────────────────┐           ┌────────────────┐           ┌────────────────┐
│                │           │                │           │                │
│   IRC client   │           │   IRC server   │           │  OAuth server  │
│                │           │                │           │                │
│ (gamja/goguma) │           │     (soju)     │           │  (meta.sr.ht)  │
│                │           │                │           │                │
└───────┬────────┘           └───────┬────────┘           └────────┬───────┘
        │                            │                             │
        │                                                          │
        │              1. Fetch OAuth server matadata              │
        ├────────────────────────────────────────────────────────► │
        │ ◄────────────────────────────────────────────────────────┤
        │                                                          │
        │                                                          │
        │              2. Redirect user to login page              │
        ├────────────────────────────────────────────────────────► │
        │ ◄────────────────────────────────────────────────────────┤
        │                     3. Get back a code                   │
        │                                                          │
        │                                                          │
        │                                                          │
        │                4. Exchange code for a token              │
        ├────────────────────────────────────────────────────────► │
        │ ◄────────────────────────────────────────────────────────┤
        │                                                          │
        │                                                          │
        │       5. Authenticate      │                             │
        │          with token        │                             │
        ├──────────────────────────► │                             │
        │                            │        6. Check token       │
        │                            ├───────────────────────────► │
        │                            │ ◄───────────────────────────┤
        │                            │      7. Get back username   │
        │                            │                             │
        │ ◄──────────────────────────┤                             │
        │                            │                             │
        │                            │                             │

Here’s a high-level overview of the interactions between the IRC client, the IRC server and the OAuth server. The IRC client and servers interact via the IRC protocol as usual, and they both interact with the OAuth server via HTTP.

  1. The user asks the IRC client to connect to “chat.sr.ht”. The client auto-discovers the OAuth server metadata to find out what the OAuth endpoints are and what features the server supports.
  2. The client redirects the user to the OAuth server login page.
  3. The user authenticates on the OAuth server login page (providing the username/password and possibly a one-time code). The OAuth server redirects back the user to the IRC client, with a code in the URL query parameters.
  4. The client grabs the code from the URL query parameters, and exchanges it for a token.
  5. The client connects to the IRC server and authenticates with the token.
  6. soju checks that the token is valid by querying the OAuth server.
  7. The OAuth server sends back the username associated with the token. soju uses that information to figure out which soju account should get selected.

Step 1 is optional: the alternative is to just hardcode all of the metadata inside the client. OAuth servers require client developers to register a client ID and client secret anyways, so it’s necessary to hardcode some metadata anyways (for now — more on that later).

Implementation

All of the above uses standards described in RFCs. This means there are already OAuth servers in the wild which support everything needed!

Step 1 uses OAuth 2.0 Authorization Server Metadata (RFC 8414). An HTTP GET request returns all of the data the client needs:

> curl https://chat.sr.ht/.well-known/oauth-authorization-server
{
	"issuer": "https://meta.sr.ht",
	"authorization_endpoint": "https://meta.sr.ht/oauth2/authorize",
	"token_endpoint": "https://meta.sr.ht/oauth2/access-token",
	"response_types_supported": ["code"],
	"grant_types_supported": ["authorization_code"],
	"introspection_endpoint": "https://meta.sr.ht/oauth2/introspect",
	"introspection_endpoint_auth_methods_supported": ["none"]
}

Readers familiar with OAuth will recognize that steps 2-4 are the usual OAuth dance defined in RFC 6749. Nothing fancy here. The client redirects the user to https://meta.sr.ht/oauth2/authorize?client_id=XXX. The OAuth server redirects back the user to the client with a ?code=YYY query parameter. The client then exchanges the code for a token via an HTTP request:

> curl \
    --data-urlencode grant_type=authorization_code \
    --data-urlencode code=YYY \
    --data-urlencode client_id=XXX \
    https://chat.sr.ht/oauth2/access-token
{
	"access_token": "asdf"
}

Something worth noting is that for Goguma, the redirect URI is a bit special. Since Goguma is a mobile app, the redirection at step 3 needs to navigate from the user’s web browser to Goguma. Following the recommendations in RFC 8252, Goguma leverages a private-use URI scheme: it sets the redirect URI to fr.emersion.goguma:/oauth2 (yes, it is a valid URI!). The web browser will open Goguma when loading that URI.

Step 5 uses the IRCv3 SASL extension in combination with the SASL OAUTHBEARER mechanism (RFC 7628). SASL PLAIN could’ve been used instead, but:

  • SASL OAUTHBEARER allows the client to ensure that the IRC server supports OAuth tokens for authentication, instead of hoping for the best and showing a vague “authentication failed” error message to the user if this assumption turns out to be wrong.
  • The SASL PLAIN RFC requires clients to specify a username, however at that point the client doesn’t know the username, it only has a token. SASL OAUTHBEARER allows the client to omit the username.

Step 6 uses OAuth 2.0 Token Introspection (RFC 7662). soju sends the token to the OAuth server, and the server replies back with some useful information:

> curl --data-urlencode token=asdf https://meta.sr.ht/oauth2/introspect
{
	"active": true,
	"username": "emersion"
}

And that’s enough for soju to associate the connection with the soju account “emersion” and send back a success response to the client!

I have patches floating around for all of the projects previously mentioned:

Future plans

Once all of the above is properly plumbed, this should already be a nice step forward! But there is also room for future improvements.

My patches currently don’t handle well token expiration. Clients should at least ask the user to re-authenticate again when a token expires. It would be nice to handle the refresh token and automatically obtain a new access token (would need to add refresh token support to meta.sr.ht).

Second, it’s a bit annoying for client developers to register their app on various OAuth servers. To remove that step, clients would need to dynamically obtain a client ID and secret from the OAuth server. The OAuth 2.0 Dynamic Client Registration Protocol (RFC 7591) can be used for this purpose. I am not sure how widely that RFC is implemented though.

Last, it would be best to avoid leaving behind some unused access tokens after the user logs out. OAuth 2.0 Token Revocation (RFC 7009) could be used by clients to clear these tokens.


Questions, comments? Please use my public inbox by sending a plain-text email to ~emersion/public-inbox@lists.sr.ht.

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