passport-negotiate

Negotiate (Kerberos) single-sign-on authentication strategy for Passport.

This Passport strategy implements authentication of users implementing "HTTP Negotiate", or SPNEGO auth-scheme, as described in RFC 4559.

For this to work, clients (browsers) must have access to a "credentials cache", which happens when logging in to a Domain in Windows, or in Linux/Unix either by using the "kinit" tool directly, or by using PAM modules which do this at login time, for example using sssd with a kerberos DC or Active Directory Domain Controller such as Samba 4.

When "Negotiate" is requested by the server, via a "WWW-Authenticate: Negotiate" header and a 401 response, the browser will obtain credentials in the form of a "ticket". The browser will then re-request the resource with the ticket data provided in the "Authorization: Negotiate .....". This happens transparently to the user.

Node.js can also be made to work as a negotiate enabled client, see this Gist.

Install

$ npm install passport-negotiate

Usage

Configure Strategy

The kerberos authentication strategy authenticates users using a username and password. The strategy requires a verify callback, which accepts the user's kerberos principal and calls done providing a user. Kerberos principals typically look like user@REALM.

var NegotiateStrategy = require("passport-negotiate");
passport.use(new NegotiateStrategy(function(principal, done) {
    User.findOne({ principal: principal }, function (err, user) {
        return done(err, user);
    });
  }
));

There are some quirks worth noting:

1. You must not use failureRedirect when using the authentication method as middleware, because the strategy must generate a 401 status response with a specific header (WWW-Authenticate: Negotiate), which won't happen if failureRedirect is used.
2. Kerberos authentication can succeed, but the supplied verify function cannot find a user object for the user. In this case, a noUserRedirect can be supplied which will in many respects work the way failureRedirect works for other strategies. The sample application examples/login demonstrates this. The strategy will set req.session.authenticatedPrincipal to the authenticated principal whenever kerberos authentication has succeeded regardless of the (in-)ability of the verify function to supply a user object.

S4U2Proxy (credential delegation)

The strategy can be configured to obtain delegated credentials on behalf of the authenticated user. Enable this by passing an options hash as the first argument to the strategy constructor:

passport.use(new NegotiateStrategy({enableConstrainedDelegation:true}, ...) 

The delegated credentials will be stored in a per-session credentials cache (the name of which will be set in req.session.delegatedCredentialsCache). Currently there is no code to monitor the lifetime of these credentials, so you will need to ensure the cache is not expired, and also to remove the cache file when the session is closed.

Note 1: S4U2Proxy support is currently WIP, and hasn't been rolled into an official release of the kerberos module that provides the underlying functionality. To get support for S4U2Proxy please use this fork. The authors are currently working on getting this code merged upstream.

Note 2: For S4U2Proxy credentials to be obtained, a credentials cache for the server principal (in addition to the keytab) must be established and maintained. For example, supposing the service keytab contains a credential for the principal HTTP/[email protected], then you could create a credentials cache in the default location using:

kinit -k HTTP/[email protected]

Alternatively, you could use k5start to ensure that the credentials cache is renewed and/or recreated so as to be valid over a long period of time

By default the service principal will NOT be enabled for S4U2Proxy. This wiki page on the kerberos website includes information on how to set up a principal to allow S4U2Proxy. Note: the UPN should be HTTP/myhost.example.com not host/myhost.example.com in all likelyhood.

Credits

• David Mansfield

License

The MIT License

Copyright (c) 2015 David Mansfield