Active Directory authentication for SaaS product

Question

After some theoretical help on the best approach for allowing a SaaS product to authenticate users against a tenant's internal Active Directory (or other LDAP) server.

The application is hosted, but a requirement exists that tenants can delegate authentication to their existing user management provider such as AD or OpenLDAP etc. Tools such as Microsoft Online's hosted exchange support corporate AD sync.

Assuming the client doesn't want to forward port 389 to their domain controller, what is the best approach for this?

Answer 1

After doing some research and talking to a few system admins who would be managing this, we've settled on an two options, which should satisfy most people. I'll describe them here for those who were also interested in the outcome.

Authentication Service installed in the origanisation's DMZ

If users wish to utilise authentication with an on-premises active directory server they will be required to install an agent in their DMZ and open port 443 to it. Our service will be configured to hit this service to perform authentication.

This service will sit in the DMZ and receive authentication requests from the SaaS application. The service will attempt to bind to active directory with these credentials and return a status to indicate success or failure.

In this instance the application's forms based authentication will not change, and the user will not be aware of the authentication behind the scenes.

OpenId

Similar to the first approach, a service will be installed in the client's DMZ, and port 443 will be opened. This will be an OpenId provider.

The SaaS application will be an OpenId consumer (already is for Facebook, Twitter, Google etc login).

When a user wishes to log in, the OpenId provider will be presented, asking them to enter their user name and password. This login screen would be served from the client's DMZ. The user would never enter their username or password into the SaaS application.

In this instance, the existing forms based authentication is replaced with the OpenId authentication from the service in the client's DNZ.

A third option that we're investigating is Active Directory Federated Services, but this is proprietary to Active Directory. The other two solutions support any LDAP based authentication across the internet.

Answer 2

Perhaps this might help…

This vendor, Stormpath, offers a service providing: user authentication, user account management, with hookups to your customers’ on-premise directories.

Answer 3

What about an LDAPS connection to the customer's user directory? They can firewall this off so that only your servers have access if they're concerned about it being public. Since it's SSL it's secure end to end. All you need from them is the certificate from their issuing CA (if it's not a public one). I struggled to get this working for an internal web project in the DMZ and there's a real lack of any guides online. So I wrote one up when I'd got it working:

http://pcloadletter.co.uk/2011/06/27/active-directory-authentication-using-ldaps/

Answer 4

Your best bet is to implement a SAML authentication for your SaaS application, and then sign up with identity providers like Okta or OneLogin. Once that's done then you can also connect it with ADFS to provide Single Sign On for your web application through Active Directory.

I'm just doing this research myself and this is what I've came across of, will have more updates once implementation is done. Hope this gives you enough keywords to do another google search

Answer 5

My understanding is that there are three possible solutions:

1. Installing something on the domain controller to capture all user changes (additions, deletions, password changes) and send updates to the remote server. Unfortunately there's no way for the website to know the initial user passwords - only new ones once they are changed.

2. Provide access for the web server to connect to your domain controller via LDAP/WIF/ADFS. This would probably mean opening incoming ports in the company's firewall to allow a specific IP.

3. Otherwise, bypass usernames/passwords and use email-based authentication instead. Users would just have to authenticate via email once every 3-6 months for each device.

I have to begin implementing this for an upcoming project and I'm seriously leaning towards option #3 for simplicity.