Usar Discourse como provedor de identidade (SSO, DiscourseConnect)

[Discourse]

Então você quer usar o Discourse como provedor de identidade para sua própria aplicação web? Ótimo! Vamos começar.

Habilitar a configuração do provedor DiscourseConnect

Em Configurações do site de administração do Discourse (/admin/site_settings), habilite a configuração enable discourse connect provider e adicione uma string secreta a discourse connect provider secrets (usada para hash de payloads SSO).

Implementar o DiscourseConnect em sua aplicação web:

• Gere um nonce aleatório nonce. Vamos chamar esse valor de NONCE. Salve-o temporariamente para que você possa verificá-lo com o valor nonce que será retornado na resposta.

• Crie um novo payload com o NONCE e uma RETURN_URL (para onde o Discourse redirecionará o usuário após a verificação). O payload deve ser assim: nonce=NONCE&return_sso_url=RETURN_URL. O host da RETURN_URL deve corresponder ao padrão de domínio que você usou ao configurar discourse connect provider secrets.

• Codifique em Base64 o payload bruto acima. Vamos chamar esse payload de BASE64_PAYLOAD

• Codifique em URL o BASE64_PAYLOAD acima. Vamos chamar esse payload de URL_ENCODED_PAYLOAD

• Gere uma assinatura HMAC-SHA256 do BASE64_PAYLOAD usando seu segredo de provedor SSO como chave, depois crie uma string hex em minúsculas a partir disso. Vamos chamar essa assinatura de HEX_SIGNATURE

Enviar solicitação de autenticação para o Discourse

Redirecione o usuário para DISCOURSE_ROOT_URL/session/sso_provider?sso=URL_ENCODED_PAYLOAD&sig=HEX_SIGNATURE

Receber resposta do Discourse:

Se as etapas acima forem feitas corretamente, o Discourse redirecionará o usuário logado para a RETURN_URL fornecida. Você receberá parâmetros de query string com sig e sso junto com algumas informações do usuário. Agora siga as etapas abaixo:

• Calcule o HMAC-SHA256 de sso usando o segredo do provedor SSO como sua chave.

• Converta sig de sua representação de string hex de volta para bytes.

• Certifique-se de que os dois valores acima sejam iguais.

• Decodifique em Base64 sso; você obterá a query string incorporada passada. Isso terá uma chave chamada nonce cujo valor deve corresponder ao nonce passado originalmente. Certifique-se de que este é o caso e exclua o nonce do seu sistema.

• Você descobrirá que essa query string também conterá um monte de informações do usuário. Use como achar melhor.

Pronto. Agora você deve ter configurado sua aplicação web para usar o Discourse como provedor SSO!

Mais Parâmetros, Mais Opções

Além de nonce e return_sso_url, o payload da solicitação tem vários parâmetros opcionais adicionais.

• prompt: Se prompt=none, então a solicitação SSO é tratada como uma solicitação de “apenas verificação”. Se o navegador/dispositivo já estiver logado no Discourse, o Discourse retornará uma resposta SSO bem-sucedida contendo informações de autenticação do usuário, como de costume. Se o navegador/dispositivo não estiver logado, o Discourse não solicitará que o usuário faça login e retornará imediatamente uma resposta SSO contendo o parâmetro failed=true em vez de informações do usuário. Isso fornece um mecanismo para consultar se o usuário está logado, sem nunca direcionar o usuário para um diálogo de login caso não esteja.

• logout: Se logout=true, então a solicitação SSO se torna uma solicitação de logout. Se um usuário estiver logado no Discourse nesse navegador/dispositivo, ele será desconectado desse dispositivo. Em ambos os casos, o Discourse redirecionará imediatamente de volta para a return_sso_url, sem sso ou sig adicionados à query string.

• require_2fa: Se require_2fa=true, o Discourse exigirá que o usuário verifique a autenticação de dois fatores antes de ser redirecionado de volta. A resposta do payload incluirá confirmed_2fa=true se o usuário concluiu com sucesso a verificação 2FA, ou no_2fa_methods=true se o usuário não tiver métodos 2FA configurados.

prompt=none e logout=true são mutuamente exclusivos; não faz sentido fornecer ambos na mesma solicitação.

Referência do Payload sso=

Parâmetros de solicitação:

• nonce: (string, obrigatório) uma string aleatória gerada de forma segura
• return_sso_url: (string, obrigatório) a URL para a qual redirecionar com a resposta
• prompt: (string, opcional) Se none, sonda o status de autenticação sem solicitar o login do usuário.
• logout: (booleano, padrão false) Se true, desconecta o usuário do Discourse.
• require_2fa: (booleano, padrão false) Se true, exige que o usuário verifique a autenticação de dois fatores antes de redirecionar de volta.

Parâmetros de resultado:

• Não há payload sso= ou assinatura em resposta a uma solicitação de logout, apenas um redirecionamento para a return_sso_url simples da solicitação.

• O payload de resultado para uma solicitação de login sempre conterá o nonce, refletido da solicitação.

• O payload de resultado também refletirá quaisquer outros parâmetros de solicitação. Não confie nesse comportamento; não é necessariamente intencional e não é um aspecto garantido da API. (Por exemplo, por que o parâmetro return_sso_url é copiado para o payload que é enviado para a return_sso_url?)

• Se a solicitação falhou ao autenticar um usuário, o payload de resultado conterá failed=true.

• Se a solicitação conseguiu autenticar um usuário, o payload de resultado conterá as credenciais/informações do usuário:

  • external_id: (string) ID do usuário do Discourse
  • username: (string) nome de usuário/identificador
  • name: (string) nome real do usuário
  • email: (string) endereço de e-mail
  • avatar_url: (string) URL CDN completa da imagem de avatar carregada pelo usuário
  • admin: (booleano) true se o usuário for Administrador, caso contrário false
  • moderator: (booleano) true se o usuário for Moderador, caso contrário false
  • groups: (string) lista de grupos (por nome) separados por vírgula aos quais o usuário pertence
  • profile_background_url: (string) URL CDN completa da imagem de fundo do perfil do usuário
  • card_background_url: (string) URL CDN completa da imagem de fundo do cartão do usuário
  • confirmed_2fa: (booleano) true se o usuário concluiu a verificação 2FA (só presente quando require_2fa=true foi solicitado)
  • no_2fa_methods: (booleano) true se o usuário não tiver métodos 2FA configurados (só presente quando require_2fa=true foi solicitado)

  name, avatar_url, profile_background_url e card_background_url podem estar ausentes se o usuário não os definiu. (Qualquer elemento com valor nil dentro do Discourse será omitido da resposta.)

Implementações oficiais do Discourse sobre “Usando o Discourse como provedor de identidade”:

• Um proxy http (usando golang) que usa o Discourse SSO para autenticar usuários (somente administradores): GitHub - discourse/discourse-auth-proxy: An http proxy that uses the DiscourseConnect protocol to authenticate users · GitHub (feito por @sam)

Implementações de comunidade contribuídas sobre “Usando o Discourse como provedor SSO”:

• Um script PHP que implementa o Discourse como provedor SSO: Discourse sso provider login · GitHub (feito 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 (requer apenas configuração):
  GitHub - Biarity/DiscourseSso: Easy, configurable Discourse SSO: GET /auth/login -> recieve a JWT with user data · GitHub

• Extensão MediaWiki (PHP):
  DiscourseSsoConsumer, a SSO extension for MediaWiki (feito 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?