Shared authentication and SSO between two webapps

Question

I have two Java wepapps potentially on different domains/servers using Spring Security for authentication. The first is handling authentication locally storing users in the application database. For the second, I would like to authenticate users using the same users accounts than the first webapp with single sign on (if a user is authenticated in the first webapp, it shouldn't have to enter his info again in the second).

I identified three potential ways to do this but it doesn't seem very straightforward:

• Shared cookies: Using a shared session cookie and the same database for the two applications. It seem relatively easy to do but the two webapps need to be on the same domain which isn't necessarily the case for my applications.

• Directory service: Using a central directory service (LDAP) which would be used by the two webapps to handle authentication. It seem pretty heavy to implement and the users can't be stored in the first webapp database anymore. The existing users accounts would need to be migrated into the LDAP and it would not be possible to create new users using the first webapp.

• OAuth: It seem to be be possible to make the first webapp handle external authentications requests by providing an OAuth api (like Google sign on kind of service). That would allow the second webapp to use this api to authenticate the users, but I'm not sure that the signin process would be totally transparent to handle single sign on. It doesn't seem very easy to implement either, as it would necessitate the development of a complete OAuth api in the first webapp.

I also looked at this service https://auth0.com that seem to provide an authentication api that can be interfaced with an external database, but I'm not sure that it can be interfaced with Spring Security and it also mandate the use of an online solution which isn't ideal. I'm not sure that it would handle single sign on either, only shared accounts.

Is there any other way to handle this use case that would be more straightforward?

Answer 1

As you mentioned, a shared cookie won't work across domains.

LDAP would give you shared credentials (single name/pw works for both systems), but not single sign on, and you notice you'll have provisioning issues.

Not knowing anything about Spring Security, odds are high you won't find a painless solution to this. Integrating SSO is fraught with workflow issues (user provisioning, password recovery, user profile maintenance, etc.)

We had a classic DB managed authentication scheme. Later, when we added LDAP support, we added the capability for "auto-provisioning". This basically consisted of having the application pull down the relevant demographics from the LDAP store during login, and simply updating fields each time user logged in. If the user didn't exist, we'd create one on the fly.

This worked well, because the rest of the application had no awareness of LDAP. It simply worked with the user profile we managed already and if it needed something from the DB, the data was there.

Later, when we integrated SSO, we just leveraged the existing LDAP logic to pull from the SSO server and do the same thing.

This workflow helped a lot with provisioning and management. We could maintained the authoritative source (LDAP, SSO), and the app just kept up. What it hindered was local editing of the user profile, so we simply disabled that. Let them view the profile, but they could go to the other systems portal for management. Inelegant, but it's a rare use case anyway, so we just muddled through it. We eventually worked out two way pushing and replication, etc. but it's a real pain if you don't need it.

You can look here if you want an overview of how to do cross domain SSO: Cross Domain Login - How to login a user automatically when transferred from one domain to another

For our SSO, we use SAML v2 Web Profile, but we ended up writing our most of our own code to pull it off.

But, bottom line, no matter what the web sites say, integrating this is non-trivial. The edge cases and workflow/help desk issues that surround it are legion. And it can be a bear to debug.

Answer 2

CAS is a good candidate indeed as a SSO system for your need and it has several CAS clients for Spring Security. You can try for free a CAS server v4.0 at CAS in the cloud: http://www.casinthecloud.com...