Usa Discourse come provider di identità (SSO, DiscourseConnect)

[Discourse]

Allora vuoi usare Discourse come fornitore di identità per la tua web app? Ottimo! Iniziamo.

Abilita l’impostazione del provider DiscourseConnect

Nelle impostazioni del sito di amministrazione di Discourse (/admin/site_settings) abilita l’impostazione enable discourse connect provider e aggiungi una stringa segreta a discourse connect provider secrets (utilizzata per l’hashing dei payload SSO).

Implementa DiscourseConnect nella tua web app:

• Genera un nonce casuale: https://en.wikipedia.org/wiki/Cryptographic_nonce. Chiamiamo questo valore NONCE. Salvalo temporaneamente in modo da poterlo verificare con il valore nonce che verrà restituito nella risposta.

• Crea un nuovo payload con il NONCE e un RETURN_URL (dove Discourse reindirizzerà l’utente dopo la verifica). Il payload dovrebbe apparire come: nonce=NONCE&return_sso_url=RETURN_URL. L’host di RETURN_URL deve corrispondere al pattern di dominio utilizzato quando si configurano i discourse connect provider secrets.

• Codifica in Base64 il payload grezzo sopra. Chiamiamo questo payload BASE64_PAYLOAD

• Codifica in URL il BASE64_PAYLOAD sopra. Chiamiamo questo payload URL_ENCODED_PAYLOAD

• Genera una firma HMAC-SHA256 da BASE64_PAYLOAD usando il tuo segreto del provider sso come chiave, quindi crea una stringa esadecimale in minuscolo da questa. Chiamiamo questa firma HEX_SIGNATURE

Invia la richiesta di autenticazione a Discourse

Reindirizza l’utente a DISCOURSE_ROOT_URL/session/sso_provider?sso=URL_ENCODED_PAYLOAD&sig=HEX_SIGNATURE

Ottieni la risposta da Discourse:

Se i passaggi precedenti sono stati eseguiti correttamente, Discourse reindirizzerà l’utente che ha effettuato l’accesso all’indirizzo RETURN_URL fornito. Riceverai parametri della stringa di query con sig e sso insieme ad alcune informazioni sull’utente. Ora segui i passaggi seguenti:

• Calcola l’HMAC-SHA256 di sso usando il segreto del provider sso come chiave.

• Converti sig dalla sua rappresentazione in stringa esadecimale di nuovo in byte.

• Assicurati che i due valori precedenti siano uguali.

• Decodifica in Base64 sso; otterrai la stringa di query incorporata passata. Questa avrà una chiave chiamata nonce il cui valore dovrebbe corrispondere al nonce passato originariamente. Assicurati che questo sia il caso e ricordati di eliminare il nonce dal tuo sistema.

• Scoprirai che questa stringa di query conterrà anche una serie di informazioni sull’utente. Usale come ritieni opportuno.

Questo è tutto. A questo punto dovresti aver configurato la tua web app per usare Discourse come provider SSO!

Più parametri, più opzioni

Oltre a nonce e return_sso_url, il payload della richiesta ha diversi parametri opzionali aggiuntivi.

• prompt: Se prompt=none, la richiesta SSO viene trattata come una richiesta di “semplice verifica”. Se il browser/dispositivo è già connesso a Discourse, Discourse restituirà una risposta SSO di successo che riporta le informazioni di autenticazione dell’utente, come di consueto. Se il browser/dispositivo non è già connesso, Discourse non chiederà all’utente di accedere ed restituirà immediatamente una risposta SSO che riporta il parametro failed=true invece delle informazioni sull’utente. Questo fornisce un meccanismo per interrogare se l’utente è connesso, senza mai reindirizzare l’utente a una finestra di dialogo di accesso se non lo è.

• logout: Se logout=true, la richiesta SSO diventa una richiesta di disconnessione. Se un utente è connesso a Discourse su quel browser/dispositivo, verrà disconnesso da quel dispositivo. In entrambi i casi, Discourse reindirizzerà immediatamente a return_sso_url, senza sso o sig aggiunti alla stringa di query.

• require_2fa: Se require_2fa=true, Discourse richiederà all’utente di verificare l’autenticazione a due fattori prima di essere reindirizzato indietro. Il payload di risposta includerà confirmed_2fa=true se l’utente ha completato con successo la verifica 2FA, oppure no_2fa_methods=true se l’utente non ha metodi 2FA configurati.

prompt=none e logout=true sono mutualmente esclusivi; non ha senso fornire entrambi nella stessa richiesta.

Riferimento al payload sso=

Parametri della richiesta:

• nonce: (stringa, obbligatorio) una stringa casuale generata in modo sicuro
• return_sso_url: (stringa, obbligatorio) l’URL a cui reindirizzare con la risposta
• prompt: (stringa, opzionale) Se none, verifica lo stato di autenticazione senza chiedere all’utente di accedere.
• logout: (booleano, predefinito false) Se true, disconnette l’utente da Discourse.
• require_2fa: (booleano, predefinito false) Se true, richiede all’utente di verificare l’autenticazione a due fattori prima di essere reindirizzato indietro.

Parametri del risultato:

• Non c’è payload sso= o firma in risposta a una richiesta di logout, solo un reindirizzamento al semplice return_sso_url della richiesta.

• Il payload del risultato per una richiesta di accesso conterrà sempre il nonce, riflesso dalla richiesta.

• Il payload del risultato rifletterà anche qualsiasi altro parametro di richiesta. Non fare affidamento su questo comportamento; non è necessariamente intenzionale e non è un aspetto garantito dell’API. (Ad esempio, perché il parametro return_sso_url viene copiato nel payload inviato a return_sso_url?)

• Se la richiesta non è riuscita ad autenticare un utente, il payload del risultato conterrà failed=true.

• Se la richiesta è riuscita ad autenticare un utente, il payload del risultato conterrà le credenziali/informazioni dell’utente:

  • external_id: (stringa) ID utente di Discourse
  • username: (stringa) nome utente/handle
  • name: (stringa) nome reale dell’utente
  • email: (stringa) indirizzo email
  • avatar_url: (stringa) URL CDN completo dell’immagine avatar caricata dall’utente
  • admin: (booleano) true se l’utente è un amministratore, altrimenti false
  • moderator: (booleano) true se l’utente è un moderatore, altrimenti false
  • groups: (stringa) elenco di gruppi (per nome) separati da virgole a cui appartiene l’utente
  • profile_background_url: (stringa) URL CDN completo dell’immagine di sfondo del profilo dell’utente
  • card_background_url: (stringa) URL CDN completo dell’immagine di sfondo della tessera dell’utente
  • confirmed_2fa: (booleano) true se l’utente ha completato la verifica 2FA (presente solo quando è stato richiesto require_2fa=true)
  • no_2fa_methods: (booleano) true se l’utente non ha metodi 2FA configurati (presente solo quando è stato richiesto require_2fa=true)

  name, avatar_url, profile_background_url e card_background_url potrebbero essere assenti se l’utente non li ha impostati. (Qualsiasi elemento con un valore nil all’interno di Discourse sarà omesso dalla risposta.)

Implementazioni ufficiali di Discourse su “Utilizzo di Discourse come fornitore di identità”:

• Un proxy http (usando golang) che utilizza Discourse SSO per autenticare gli utenti (solo amministratori): GitHub - discourse/discourse-auth-proxy: An http proxy that uses the DiscourseConnect protocol to authenticate users · GitHub (realizzato da @sam)

Implementazioni contribuite dalla community su “Utilizzo di Discourse come provider SSO”:

• Uno script PHP che implementa Discourse come provider SSO: Discourse sso provider login · GitHub (realizzato da @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 (richiede solo configurazione):
  GitHub - Biarity/DiscourseSso: Easy, configurable Discourse SSO: GET /auth/login -> recieve a JWT with user data · GitHub

• Estensione MediaWiki (PHP):
  DiscourseSsoConsumer, a SSO extension for MediaWiki (realizzato da @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?