mod_http_oauth2

Introduction

This module implements an OAuth2/OpenID Connect (OIDC) Authorization Server on top of Prosody’s usual internal authentication backend.

OAuth and OIDC are web standards that allow you to provide clients and third-party applications limited access to your account, without sharing your password with them.

With this module deployed, software that supports OAuth can obtain “access tokens” from Prosody which can then be used to connect to XMPP accounts using the OAUTHBEARER SASL mechanism or via non-XMPP interfaces such as mod_rest.

Although this module has been around for some time, it has recently been significantly extended and largely rewritten to support OAuth/OIDC more fully.

As of April 2023, it should be considered alpha stage. It works, we have tested it, but it has not yet seen wider review, testing and deployment. At this stage we recommend it for experimental and test deployments only. For specific information, see the deployment notes section below.

Known client implementations:

Support for OAUTHBEARER has been added to the Lua XMPP library, verse. If you know of additional implementations, or are motivated to work on one, please let us know! We’d be happy to help (e.g. by providing a test server).

Standards support

Notable supported standards:

Configuration

Interface

The module presents a web page to users to allow them to authenticate when a client requests access. Built-in pages are provided, but you may also theme or entirely override them.

This module honours the site_name configuration option that is also used by a number of other modules:

site_name = "My XMPP Server"

To provide custom templates, specify the path to the template directory:

oauth2_template_path = "/etc/prosody/custom-oauth2-templates"

If you know what features your templates use use you can adjust the Content-Security-Policy header to only allow what is needed:

oauth2_security_policy = "default-src 'self'" -- this is the default

Token parameters

The following options configure the lifetime of tokens issued by the module. The defaults are recommended.

oauth2_access_token_ttl = 3600 -- one hour
oauth2_refresh_token_ttl = 604800 -- one week

Dynamic client registration

To allow users to connect any compatible software, you should enable dynamic client registration.

Dynamic client registration can be enabled by configuring a JWT key. Algorithm defaults to HS256, lifetime defaults to forever.

oauth2_registration_key = "securely generated JWT key here"
oauth2_registration_algorithm = "HS256"
oauth2_registration_ttl = nil -- unlimited by default

Registering a client is described in RFC7591.

In addition to the requirements in the RFC, the following requirements are enforced:

client_name
MUST be present, is shown to users in consent screen.
client_uri
MUST be present and MUST be a https:// URL.
redirect_uris

MUST contain at least one valid URI. Different rules apply depending on the value of application_type, see below.

application_type

Optional, defaults to web. Determines further restrictions for redirect_uris. The following values are supported:

web (default)
For web clients. With this, redirect_uris MUST be https:// URIs and MUST use the same hostname part as the client_uri.
native

For native e.g. desktop clients etc. redirect_uris MUST match one of:

  • Loopback HTTP URI, e.g. http://127.0.0.1/ or http://[::1]
  • Application-specific scheme, e.g. com.example.app:/
  • The special OOB URI urn:ietf:wg:oauth:2.0:oob
tos_uri, policy_uri
Informative URLs pointing to Terms of Service and Service Policy document MUST use the same scheme (i.e. https://) and hostname as the client_uri.
Registration Examples

In short registration works by POST-ing a JSON structure describing your client to an endpoint:

curl -sSf https://xmpp.example.net/oauth2/register \
    -H Content-Type:application/json \
    -H Accept:application/json \
    --data '
{
   "client_name" : "My Application",
   "client_uri" : "https://app.example.com/",
   "redirect_uris" : [
      "https://app.example.com/redirect"
   ]
}
'

Another example with more fields:

curl -sSf https://xmpp.example.net/oauth2/register \
    -H Content-Type:application/json \
    -H Accept:application/json \
    --data '
{
   "application_type" : "native",
   "client_name" : "Desktop Chat App",
   "client_uri" : "https://app.example.org/",
   "contacts" : [
      "support@example.org"
   ],
   "policy_uri" : "https://app.example.org/about/privacy",
   "redirect_uris" : [
      "http://localhost:8080/redirect",
      "org.example.app:/redirect"
   ],
   "scope" : "xmpp",
   "software_id" : "32a0a8f3-4016-5478-905a-c373156eca73",
   "software_version" : "3.4.1",
   "tos_uri" : "https://app.example.org/about/terms"
}
'

Supported flows

Various flows can be disabled and enabled with allowed_oauth2_grant_types and allowed_oauth2_response_types:

-- These examples reflect the defaults
allowed_oauth2_grant_types = {
    "authorization_code"; -- authorization code grant
    "device_code";
    -- "password"; -- resource owner password grant disabled by default
}

allowed_oauth2_response_types = {
    "code"; -- authorization code flow
    -- "token"; -- implicit flow disabled by default
}

The Proof Key for Code Exchange mitigation method is required by default but can be made optional:

oauth2_require_code_challenge = false -- default is true

Further, individual challenge methods can be enabled or disabled:

-- These reflects the default
allowed_oauth2_code_challenge_methods = {
    -- "plain"; -- insecure but backwards-compatible
    "S256";
}

Policy documents

Links to Terms of Service and Service Policy documents can be advertised for use by OAuth clients:

oauth2_terms_url = "https://example.com/terms-of-service.html"
oauth2_policy_url = "https://example.com/service-policy.pdf"
-- These are unset by default

Deployment notes

Access management

This module does not provide an interface for users to manage what they have granted access to their account! (e.g. to view and revoke clients they have previously authorized). It is recommended to join this module with mod_client_management to provide such access. However, at the time of writing, no XMPP clients currently support the protocol used by that module. We plan to work on additional interfaces in the future.

Scopes

OAuth supports “scopes” as a way to grant clients limited access.

There are currently no standard scopes defined for XMPP. This is something that we intend to change, e.g. by definitions provided in a future XEP. This means that clients you authorize currently have to choose between unrestricted access to your account (including the ability to change your password and lock you out!) and zero access. So, for now, while using OAuth clients can prevent leaking your password to them, it is not currently suitable for connecting untrusted clients to your account.

As a first step, the xmpp scope is supported, and corresponds to whatever permissions the user would have when logged in over XMPP.

Further, known Prosody roles can be used as scopes.

OpenID scopes such as openid and profile can be used for “Login with XMPP” without granting access to more than limited profile details.

Compatibility

Requires Prosody trunk (April 2023), not compatible with Prosody 0.12 or earlier.

Installation

With the plugin installer in Prosody 0.12 you can use:

sudo prosodyctl install --server=https://modules.prosody.im/rocks/ mod_http_oauth2

For earlier versions see the documentation for installing 3rd party modules

Latest changes