Can application get TGT ticket?

[Yan Zhou]

Hello, 

CAS protocol does not let the apps (CAS client) get TGT ticket. We have a need for that.

We have two web apps, both are casified in CAS 4.1.X. One web app has AngularJS (Javascript) front end, and, the other webapp is UI-Less, it just offers REST services. 

Javascript code in App A wants to call REST API in App B.  We run into problem with CORS, etc. But, even after CORS are enabled, still run into trouble.

So, the thought is, if Javascript code can get hold of TGT after user login to the app. A, then, JS code call use CAS REST API to authenticate against the 2nd app (the UI-less REST Services). 

Is that a bad idea, and how is that possible?

Yan

[Yaroslav Panych]

You can export TGT in serviceValidate endpoint. We do that there(in 4.0.x)

[Carlos M. Fernández]

The application should never have the TGT – that opens up a big security vulnerability.

 

Instead you should look into using Proxy CAS, with which a service can transmit identity to another service.

 

https://wiki.jasig.org/display/CAS/Proxy+CAS+Walkthrough

 

Best regards,

--

Carlos.

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[William G. Thompson, Jr.]

You should take a look at Proxy Granting Tickets, which allow an
application to securely call another app on behalf of a user.

http://stackoverflow.com/questions/6368358/restful-cas-client-and-proxy-granting-tickets
https://wiki.jasig.org/display/CAS/Proxy+CAS+Walkthrough

Best,
Bill

[Pascal Rigaux]

Hi,

Solutions:
- proxy CAS: As the proxy ticket can only be validated once, you will need to cache the ticket, or create your own session
- JWT: create a JWT and check it on app B.
- oauth
- JSONP login on app B. We are using this quite a lot. Simple and works great.
Commits implementing this on angular-seed : https://github.com/prigaux/angular-seed/commits/master
and especially the first one: https://github.com/prigaux/angular-seed/commit/27eae718ff6fd3206f60926317c7a24ddfd79b68
I wrote some doc on this, alas in french: http://prigaux.github.io/presentation-web-widgets-cas-jsonp/index.html#/7

Happy CAS,
cu

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DSIUN-SAS (service applications et services numériques)
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[Yan Zhou]

thanks for the feedback.

Unfortunately, we cannot use Proxy Authentication, due to PCI implication. A non PCI-compliant App proxy a PCI (credit card) service, that would not be allowed by PCI standards.

The reason we run into problem with CAS protected REST services (App B, no UI), is that Ajax somehow does not handle redirect (even after I enable CORS). Browser does it fine, but fails when Ajax tries to access the REST endpoint without an application session in place, thus triggers CAS login flow with all the redirect.

I do not see how OAuth solve that problem. Does that requires a Login page UI to redirect to and back, would not that run into the same problem with Ajax?

Can you elaborate on JSONP? Would app. B now have to know user's password?  CAS is nice because the application does not see user's password, only CAS server does.

Thx,

Yan

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Pascal Rigaux

Expert en développement et déploiement d'applications
DSIUN-SAS (service applications et services numériques)
Université Paris 1 Panthéon-Sorbonne  -  Centre Pierre Mendès France (PMF)
B 402 - 90, rue de Tolbiac -  75634 PARIS CEDEX 13 - FRANCE
Tél : 01 44 07 86 59

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[Ray Bon]

Yan,

If I understand correctly, you have deployed App A and App B. You are not able nor willing to change CAS config on App B because it breaches PCI compliance.
It seems odd that PCI compliance would allow any user access but not allow a proxy.
Did you create app A or are both apps from third party vendors?

If app B needs to know the user that is sending the request, then you will have to use clearpass, https://apereo.github.io/cas/4.0.x/integration/ClearPass.html.
If app B only needs to have an authenticated user, then perhaps App A can perform the log in on behalf of all users. The Ajax calls would go from App A UI to App A service that makes the REST calls.

What do the creators of App B suggest for authentication?

Ray

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[Yan Zhou]

Hello,

The basic problem is that CAS login flow works in browser. However, because of the series of redirect involved, CAS login flow does not seem to work in Ajax. 

This is my set-up:  App A has UI with AngularJS and backend,  App B has NO UI and it offers REST services including Credit card services. Both are casified and we have total control.  We are trying to use CAS to protect REST services in B.

App B must be deployed in a PCI environment, but App A does not. If App A was going to talk to or proxy App B, that is not allowed by PCI standards, because A would see credit card info. passing along to B, but A is not deployed in PCI environment. 

The idea is for UI (AngularJS) to talk to App B directly, so that there is not anything else between user and PCI environment. I am making the point that Proxy Authentication is not a solution here. 

Here is what I am trying to do: user from Internet first login to CAS and goes to App A's UI.  From there, javascript makes Ajax call to App B's REST service.  This results in a series of redirect before an application session in B is established and REST call can proceed. In Ajax, it is failing. 

Thanks,

Yan

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[Dmitriy Kopylenko]

Just to be clear - CAS protocol was never designed to work with Ajax and REST resources (non-interactive service-to-service)

Best,

D.

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[Pascal Rigaux]

On 02/11/2016 21:12, Yan Zhou wrote:

> Can you elaborate on JSONP?
> Would app. B now have to know user's password?

No need.
JSONP is pre-CORS. It has some limitations compared to Ajax, but some useful possibilities, like auto CAS login.
Here is an example of adding auto login in angularJS:
https://github.com/prigaux/angular-seed/commit/4d51d23280eb959a3d1773b2fcc69c4cf50ccd88

By the way, another simpler solution is to allow restricted redirect after login in app B.
Make the user go to:
- https://b/login?redirect=https://a/
which redirects to (normal CAS login)
- https://cas/login?service= https://b/login?redirect=https://a/
which redirects to
- https://b/login?redirect=https://a/&ticket=xxxx
=> set-cookie of application b
which redirects to
- https://a
this app can do AJAX request https://b/rest
=> works since cookie of app B

cu

[Yan Zhou]

Thanks for the suggestions.

Going with my scenario, first, user logins to A via CAS, then, AngularJS calls B.  There is no session for B, so the REST call returns 401, however, we should not be asking user to login again, since he already logged into A.  A and B are SSO via CAS.

What we need to do is to get CAS login flow to work in Ajax just as it is in browser. 

The issue with redirect you provided is when B session expires. A won't know, thus, there is not a way to repeat the redirect trick. Further, we likely will have B, C, E all as REST services backend, that gets a little hard to manage.

Thanks,

Yan

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