File

---
labels:
- Stage-Alpha
rockspec:
  build:
    copy_directories:
    - html
summary: OAuth 2.0 Authorization Server API
---

## Introduction

This module implements an [OAuth2](https://oauth.net/2/)/[OpenID Connect
(OIDC)](https://openid.net/connect/) provider HTTP frontend 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][rfc7628] 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](#deployment-notes)
below.

Known client implementations:

-   [example shell script for mod_rest](https://hg.prosody.im/prosody-modules/file/tip/mod_rest/example/rest.sh)
-   *(we need you!)*

Support for [OAUTHBEARER][rfc7628] has been added to the Lua XMPP
library, [verse](https://code.matthewwild.co.uk/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:

- [RFC 6749: The OAuth 2.0 Authorization Framework](https://www.rfc-editor.org/rfc/rfc6749)
- [RFC 7009: OAuth 2.0 Token Revocation](https://www.rfc-editor.org/rfc/rfc7009)
- [RFC 7591: OAuth 2.0 Dynamic Client Registration](https://www.rfc-editor.org/rfc/rfc7591.html)
- [RFC 7628: A Set of Simple Authentication and Security Layer (SASL) Mechanisms for OAuth](https://www.rfc-editor.org/rfc/rfc7628)
- [RFC 7636: Proof Key for Code Exchange by OAuth Public Clients](https://www.rfc-editor.org/rfc/rfc7636)
- [OpenID Connect Core 1.0](https://openid.net/specs/openid-connect-core-1_0.html)
- [OpenID Connect Discovery 1.0](https://openid.net/specs/openid-connect-discovery-1_0.html) (_partial, e.g. missing JWKS_)
- [OpenID Connect Dynamic Client Registration 1.0](https://openid.net/specs/openid-connect-registration-1_0.html) 

## 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:

```lua
site_name = "My XMPP Server"
```

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

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

Some templates support additional variables, that can be provided by the
`oauth2_template_style` option:

```lua
oauth2_template_style = {
  background_colour = "#ffffff";
}
```

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

```lua
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.

```lua
oauth2_access_token_ttl = 86400 -- 24 hours
oauth2_refresh_token_ttl = nil -- unlimited unless revoked by the user
```

### 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.

```lua
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](https://www.rfc-editor.org/rfc/rfc7591.html).

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`:

    `web`
    :   `redirect_uris` **MUST** be `https://` URIs and **MUST** use the
        same hostname part as the `client_uri`.

    `native`

    :   `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`

`application_type`

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

    `web` *(default)*
    :   For web clients.

    `native`
    :   For native e.g. desktop clients etc.

`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 Example

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

``` bash
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"
   ]
}
'
```

### Supported flows

-   Authorization Code grant, optionally with Proof Key for Code Exchange
-   Resource owner password grant
-   Implicit flow *(disabled by default)*
-   Refresh Token grants

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

```lua
-- These examples reflect the defaults
allowed_oauth2_grant_types = {
	"authorization_code"; -- authorization code grant
	"password"; -- resource owner password grant
}

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

The [Proof Key for Code Exchange][RFC 7636] mitigation method is
optional by default but can be made required:

```lua
oauth2_require_code_challenge = true -- default is false
```

Further, individual challenge methods can be enabled or disabled:

```lua
-- These reflects the default
allowed_oauth2_code_challenge_methods = {
    "plain"; -- the insecure one
    "S256";
}
```

### Policy documents

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

```lua
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.