Usar Discourse como proveedor de identidad (SSO, DiscourseConnect)

[Discourse]

Entonces, ¿quieres usar Discourse como proveedor de identidad para tu propia aplicación web? ¡Genial! Empecemos.

Habilitar la configuración del proveedor DiscourseConnect

En la configuración de administración del sitio de Discourse (/admin/site_settings), habilita la configuración enable discourse connect provider y agrega una cadena secreta a discourse connect provider secrets (utilizada para hashear las cargas útiles de SSO).

Implementar DiscourseConnect en tu aplicación web:

• Genera un nonce aleatorio. Llamemos a este valor NONCE. Guárdalo temporalmente para poder verificarlo con el valor nonce que se devolverá en la respuesta.

• Crea una nueva carga útil con el NONCE y una RETURN_URL (a donde Discourse redirigirá al usuario después de la verificación). La carga útil debe verse así: nonce=NONCE\u0026return_sso_url=RETURN_URL. El host de RETURN_URL debe coincidir con el patrón de dominio que usaste al configurar discourse connect provider secrets.

• Codifica en Base64 la carga útil sin procesar anterior. Llamemos a esta carga útil BASE64_PAYLOAD.

• Codifica en URL la BASE64_PAYLOAD anterior. Llamemos a esta carga útil URL_ENCODED_PAYLOAD.

• Genera una firma HMAC-SHA256 a partir de BASE64_PAYLOAD usando tu secreto de proveedor sso como clave, luego crea una cadena hexadecimal en minúsculas a partir de esto. Llamemos a esta firma HEX_SIGNATURE.

Enviar solicitud de autenticación a Discourse

Redirige al usuario a DISCOURSE_ROOT_URL/session/sso_provider?sso=URL_ENCODED_PAYLOAD\u0026sig=HEX_SIGNATURE

Recibir respuesta de Discourse:

Si los pasos anteriores se realizaron correctamente, Discourse redirigirá al usuario que ha iniciado sesión a la RETURN_URL proporcionada. Recibirás parámetros de cadena de consulta con sig y sso junto con algo de información del usuario. Ahora sigue los siguientes pasos:

• Calcula el HMAC-SHA256 de sso usando el secreto del proveedor sso como tu clave.

• Convierte sig de su representación de cadena hexadecimal de vuelta a bytes.

• Asegúrate de que los dos valores anteriores sean iguales.

• Decodifica en Base64 sso; obtendrás la cadena de consulta incrustada pasada. Esto tendrá una clave llamada nonce cuyo valor debe coincidir con el nonce pasado originalmente. Asegúrate de que este sea el caso y asegúrate de eliminar el nonce de tu sistema.

• Descubrirás que esta cadena de consulta también contiene mucha información del usuario. Úsala como mejor te parezca.

Eso es todo. ¡A estas alturas deberías haber configurado tu aplicación web para usar Discourse como proveedor SSO!

Más Parámetros, Más Opciones

Además de nonce y return_sso_url, la carga útil de la solicitud tiene varios parámetros opcionales adicionales.

• prompt: Si prompt=none, entonces la solicitud SSO se trata como una solicitud de “solo verificación”. Si el navegador/dispositivo ya ha iniciado sesión en Discourse, Discourse devolverá una respuesta SSO exitosa con información de autenticación del usuario, como de costumbre. Si el navegador/dispositivo no ha iniciado sesión, entonces Discourse no le pedirá al usuario que inicie sesión, y devolverá inmediatamente una respuesta SSO con el parámetro failed=true en lugar de la información del usuario. Esto proporciona un mecanismo para consultar si el usuario ha iniciado sesión, sin dirigir nunca al usuario a un diálogo de inicio de sesión si no lo está.

• logout: Si logout=true, entonces la solicitud SSO se convierte en una solicitud de cierre de sesión. Si un usuario ha iniciado sesión en Discourse en ese navegador/dispositivo, se cerrará la sesión en ese dispositivo. En cualquier caso, Discourse redirigirá inmediatamente a la return_sso_url, sin sso o sig agregados a la cadena de consulta.

• require_2fa: Si require_2fa=true, entonces Discourse requerirá que el usuario verifique la autenticación de dos factores antes de ser redirigido de vuelta. La carga útil de respuesta incluirá confirmed_2fa=true si el usuario completó con éxito la verificación 2FA, o no_2fa_methods=true si el usuario no tiene métodos 2FA configurados.

prompt=none y logout=true son mutuamente excluyentes; no tiene sentido proporcionar ambos en la misma solicitud.

Referencia de carga útil sso=

Parámetros de solicitud:

• nonce: (string, requerido) una cadena aleatoria generada de forma segura
• return_sso_url: (string, requerido) la URL a la que redirigir con la respuesta
• prompt: (string, opcional) Si es none, sonda el estado de autenticación sin solicitar al usuario que inicie sesión.
• logout: (boolean, predeterminado false) Si es true, cierra la sesión del usuario en Discourse.
• require_2fa: (boolean, predeterminado false) Si es true, requiere que el usuario verifique la autenticación de dos factores antes de redirigir de vuelta.

Parámetros de resultado:

• No hay carga útil sso= ni firma en respuesta a una solicitud de cierre de sesión, solo una redirección a la return_sso_url simple de la solicitud.

• La carga útil de resultado para una solicitud de inicio de sesión siempre contendrá el nonce, reflejado desde la solicitud.

• La carga útil de resultado también reflejará cualquier otro parámetro de solicitud. No confíes en este comportamiento; no es necesariamente intencional y no es un aspecto garantizado de la API. (Por ejemplo, ¿por qué el parámetro return_sso_url se copia en la carga útil que se envía a la return_sso_url?)

• Si la solicitud falló al autenticar a un usuario, la carga útil de resultado contendrá failed=true.

• Si la solicitud logró autenticar a un usuario, la carga útil de resultado contendrá credenciales/información del usuario:

  • external_id: (string) ID de usuario de Discourse
  • username: (string) nombre de usuario/identificador
  • name: (string) nombre real del usuario
  • email: (string) dirección de correo electrónico
  • avatar_url: (string) URL CDN completa de la imagen de avatar subida del usuario
  • admin: (boolean) true si el usuario es un administrador, de lo contrario false
  • moderator: (boolean) true si el usuario es un moderador, de lo contrario false
  • groups: (string) lista separada por comas de grupos (por nombre) a los que pertenece el usuario
  • profile_background_url: (string) URL CDN completa de la imagen de fondo del perfil del usuario
  • card_background_url: (string) URL CDN completa de la imagen de fondo de la tarjeta del usuario
  • confirmed_2fa: (boolean) true si el usuario completó la verificación 2FA (solo presente cuando se solicitó require_2fa=true)
  • no_2fa_methods: (boolean) true si el usuario no tiene métodos 2FA configurados (solo presente cuando se solicitó require_2fa=true)

  name, avatar_url, profile_background_url y card_background_url pueden estar ausentes si el usuario no ha establecido estos. (Cualquier elemento con un valor nil dentro de Discourse se omitirá de la respuesta).

Implementaciones oficiales de Discourse de “Uso de Discourse como proveedor de identidad”:

• Un proxy http (usando golang) que utiliza Discourse SSO para autenticar usuarios (solo administradores): GitHub - discourse/discourse-auth-proxy: An http proxy that uses the DiscourseConnect protocol to authenticate users · GitHub (hecho por @sam)

Implementaciones de la comunidad de “Uso de Discourse como proveedor SSO”:

• Un script PHP que implementa Discourse como proveedor SSO: Discourse sso provider login · GitHub (hecho por @paxmanchris)

• Ruby:
  GitHub - AstonJ/sso_with_discourse: Implementation in ruby for https://meta.discourse.org/t/using-discourse-as-a-sso-provider/32974 · GitHub

• Erlang:
  https://github.com/reverendpaco/discourse-as-sso-erlang

• Node.js:
  GitHub - edhemphill/passport-discourse: A Passport strategy for authenticating using a Discourse forum · GitHub
  GitHub - ArmedGuy/discourse_sso_node: npm package for Discourse SSO login features. · GitHub

• ASP.NET Core (solo requiere configuración):
  GitHub - Biarity/DiscourseSso: Easy, configurable Discourse SSO: GET /auth/login -> recieve a JWT with user data · GitHub

• Extensión MediaWiki (PHP):
  DiscourseSsoConsumer, a SSO extension for MediaWiki (hecho por @mdoggydog)

[jamesmarkcook (James Cook)]

Great how to, thanks.

FYI, the term ‘nonce’ has an unfortunate meaning in Britain.

[gogo52cn (david)]

I wrote a class to implement the process in Ruby. I use it to work with devise in my web application.

https://github.com/gogo52cn/sso_with_discourse

[ianmackinnon]

@techAPJ

Compute the HMAC-SHA256 of sso using sso_secret as your key.

sso seems to have a trailing newline which needs to be included when sent to the HMAC function, so it’s important to make sure that SSO consumer applications don’t strip whitespace from these query arguments.

[geneles (Michael Geneles)]

Our app users get their own subdomains. Is there a way to implement this with variable SSO urls?

[sam (Sam Saffron)]

interesting, this is tricky you would need to monkey patch this in, or better still make core extensible in this way and add a plugin.

[reverend_paco (Daniel Eklund)]

Hello,

I have created an Erlang implementation for encoding/decoding the payloads described in this specification. You can find it here:
https://github.com/reverendpaco/discourse-as-sso-erlang
Feedback is welcome.

Thanks to @mpalmer on another thread for setting me straight.

As I put together this implementation, I realized that the specification does not say too much about a few things:

1. the user information that is returned in the query parameters,
2. what happens when a user is not found

When I got around to testing I found the answers, and then confirmed by looking at the code, here: discourse/app/controllers/session_controller.rb at main · discourse/discourse · GitHub

I shall assume that in regards to 1. that while new user information may be added, that none of these values (“name”,“username”,“email”,“external_id”, etc) will be removed. This is just as important, contractually as what is described in the main post.

One piece of feedback I’d like to give the Discourse team is that it would be nice to add a means to optionally return back to the calling application in the case of a missing user.

Currently, at line 51 a non-logged-in or non-registered user will be forwarded to the Discourse login page. While this can be useful, I would rather programmatically have the option to learn that this person has not yet logged in (or registered) and give them the opportunity on my site to continue anonymously.

I can imagine something like this:

DISCOURSE_ROOT_URL/session/sso_provider?
sso=URL_ENCODED_PAYLOAD&sig=HEX_SIGNATURE&
returnBackIfUserMissing=true

and then the Discourse site sending back to the return_sso_url with either a special header, or an attribute, rather than redirecting to /login.

This change should be backwards compatible.
I’m new here, so if this is something that could be contributed via a pull-request, please tell me and I could take a shot at it next week.

thanks,
daniel

[sam (Sam Saffron)]

@reverend_paco

One piece of feedback I’d like to give the Discourse team is that it would be nice to add a means to optionally return back to the calling application in the case of a missing user.

Sure, totally open to add another option to the payload you send us for create_new=false PR welcome.

[reverend_paco (Daniel Eklund)]

added a PR for this

Optional 'no_user_found_return_sso_url' parameter for using Discourse as SSO

Commit-Message:

Implemented an optional 'no_user_found_return_sso_url' parameter to be called
 by the client when client is using Discourse as an SSO and wants Discourse to 
redirect back to a place of the client's choosng when a user is not found.

Currently, the Discourse as an SSO implementation checks the cookies _t and
 _session_forum to see if the user is registered and present in the database 
(_t is the token that is located in the users table). If a user is not found, 
the current implemenation forwards to the forum's /login URL. This behavior 
may be what the client wants, but it would be good to give an option to the 
client to send somewhere else.

This commit allows the client to embed an optional 'no_user_found_return_sso_url' 
parameter in the payload, prior to base64 and URL-encoding. If the Discoure SSO
endpoint detects that this parameter is present in the payload (and has a non-empty
value) the Discourse server will redirect to this new location if it does not detect the 
user. If this parameter is not present, then the redirection to /login will take place 
as it currently does.

Additionally, as the client may choose to use the same URL for
'no_user_found_return_sso_url' as for 'return_url', this commit introduces a new 
query-string name-value pair to be sent back to the client 'no_user_found_return_sso_url' 
location. This parameter 'user_found' will ALWAYS be sent back to the client, either when 
the user is found and 'return_url' is used or when the user is not found 
'no_user_found_return_sso_url' is used (values will be 'true' and 'false' respectively).

thanks,
daniel

[fantasticfears (Erick Guan)]

Nice work

redirect_to can be routed to a url with parameters. But isn’t a create_new=false enough? Or whatever name it is. You’ll get nonce and the flag back.

[reverend_paco (Daniel Eklund)]

@fantasticfears

But isn’t a create_new=false enough? Or whatever name it is. You’ll get nonce and the flag back.

I wanted to give the client the flexibility of sending a failure to a different URL than the success url (return_url). With complicated SSO architectures, this might be a requirement. (Selfishly, I wanted to make my return endpoint code less convoluted – i.e. on my side I have two codebases at /sso for success and /sso_failure for failure).

Implicitly there are already two URLs (return_url for success and ‘/login’ for failure) – I didn’t want to lose that.

So just to be clear, the payload you send to the Discourse endpoint should have both return_url and no_user_found_return_sso_url if you want Discourse to send it back when no user is found. It should have return_url only if you are ok with Discourse forwarding to /login.

Should look like this:

1.If you want Discourse to forward to login if no user found, then:

PAYLOAD = return_url=mydomain.com/clientendpoint&nonce=xE787euK
2. If you want Discourse to send back to you to the same endpoint for failure as success:

PAYLOAD = no_user_found_return_sso_url=mydomain.com/clientendpoint&return_url=mydomain.com/clientendpoint&nonce=xE787euK
3. If you want Discourse to send back to you to a different endpoint as success:

PAYLOAD = no_user_found_return_sso_url=sub.mydomain.com/handleNewUser&return_url=mydomain.com/clientendpoint&nonce=xE787euK

Potentially a bit over-engineered, but that was my thought process.

[fantasticfears (Erick Guan)]

@reverend_paco

I wanted to give the client the flexibility of sending a failure to a different URL than the success url (return_url). With complicated SSO architectures, this might be a requirement. (Selfishly, I wanted to make my return endpoint code less convoluted – i.e. on my side I have two codebases at /sso for success and /sso_failure for failure).

To be clear, it’s not user_not_found, it’s not logged in.

It’s about protocol not engineering in the first place. Given two endpoints, you have to deal with two possible endpoints. In both cases you must validate the nonce and destroy it. It’s a hurdle not benefit.

In extreme case, a client can ask Discourse several times with/without session (current_user), thus you would get n responses in each endpoints. It would be twice as hard to secure it due to changing cookies on your end.

[reverend_paco (Daniel Eklund)]

@fantasticfears

It’s about protocol not engineering in the first place.

Completely agree on protocol over engineering. Hence, my submission.

The semantics are equivalent to an if-else block, or more generally a case/switch block. result_url is our true condition, and user_not_found_url is our else block. If we didn’t provide it, we would force the client to have to deal with the ‘failure’ condition in the same codebase/endpoint – and for 90% of the people, this will be fine.

90% of people who want Discourse to return back to them will set return_url and user_not_found_url to be exact same thing. This bears repeating, and really renders the motivations for the 10% moot.

90% of the time you will make return_url and user_not_found_url the exact same thing. These 90%-ers will use their JSESSIONID/ PHPSESSID/ ASPSESSIONID /_session to look up the returned encoded nonce in their framework-supplied session-store and engineer accordingly.

7% of people will be happy to pass it to a different URL on their same app-server, which does some decoration (servlet-chains anyone?) or routing, but still looks up the nonce in their session.

3% will have some complicated polyglotish system that uses a distributed session store (like memcache) to store sessions for different app servers implemented in different legacy codebases. It’s up to them to store/invalidate the nonce across these different systems.

I realize I might not have been completely clear, but the user_not_found_url still receives the sso and sig parameters, just like the return_url.

So, if you are the 90% scenario, when you get the payload and verify/decode it, you will find the parameter user_found=false|true to know why it’s coming back to you.

[reverend_paco (Daniel Eklund)]

@fantasticfears, as per your recommendation on the PR, I have renamed the attribute from user_not_found_url to return_sso_unlogged_in_url.

[thomasschmit]

Great job !

Do you know how it possible to adapt it to GitLab in order to allow the Discourse users to directly login there?

[edhemphill (Ed)]

Hey folks, I could not find anything, so I created a npm for Discourse auth using Passport for node.js.

It’s here, and in npm if anyone needs it:

GitHub - edhemphill/passport-discourse: A Passport strategy for authenticating using a...

(really appreciate the team’s work, we’ve been a user since the very early days @ talk.wigwag.com)

[reverend_paco (Daniel Eklund)]

@sam,

I have submitted a reply back to your rejection of the PR:
Optional 'no_user_found_return_sso_url' parameter for using Discourse as SSO by reverendpaco · Pull Request #4211 · discourse/discourse · GitHub

As I have been relying on my patched version of discourse for these months, I would be interested in convincing you as to my need.

[reverend_paco (Daniel Eklund)]

@reverend_paco

@sam,

I have submitted a reply back to your rejection of the PR:
Optional 'no_user_found_return_sso_url' parameter for using Discourse as SSO by reverendpaco · Pull Request #4211 · discourse/discourse · GitHub

As I have been relying on my patched version of discourse for these months, I would be interested in convincing you as to my need.

If this PR is going to be rejected, could you explain what I can do to get the functionality that I need?

[Sveinn_S (Sveinn Svavarsson)]

Does anyone know of a wordpress plugin that works with discourse as the SSO provider?