Passport-UWShib

Passport authentication strategy that works with the University of Washington's Shibboleth single-sign on service. This uses the fabulous passport-saml module for all the heavy lifting, but sets all the default options so that it works properly with the UW Shibboleth Identity Provider (IdP).

Note that in order to use the UW IdP for authentication, you must register your server. During the registration process, it will attempt to gather your server's metadata via the route /Shibboleth.sso/Metadata. This module provides an implementation for that route, but you have to set that up in your main server script (see /example/server.js).

While registering, you must also specify which user profile attributes you want. See the Guide to Attributes Available from the UW IdP for more information.

Installation

npm install passport-uwshib

or if using a package.json file, add this line to your dependencies hash:

"passport-uwshib": "*"

and do an npm install or npm update to get the most current version.

Usage

There is a fully-working example server script in /example/server.js, and an associated package.json, which you can use to install all the necessary packages to make the example script run (express, express middleware, passport, etc.). Refer to that as I explain what it is doing.

This module provides a Strategy for the Passport framework, which is typically used with Express. Thus, there are several modules you need to require in your server script in addition to this module.

var http = require('http');                     //http server
var https = require('https');                   //https server
var fs = require('fs');                         //file system
var express = require("express");               //express middleware
var morgan = require('morgan');                 //logger for express
var bodyParser = require('body-parser');        //body parsing middleware
var cookieParser = require('cookie-parser');    //cookie parsing middleware
var session = require('express-session');       //express session management
var passport = require('passport');             //authentication middleware
var uwshib = require('passport-uwshib');        //UW Shibboleth auth strategy

The example script then gets the server's domain name from an environment variable. This allows you to run the example script without modification. Simply export a value for DOMAIN and run the script.

export DOMAIN=mydomain.uw.edu
node server.js

You can also override the default HTTP and HTTPS ports if you wish by specifying HTTPPORT and HTTPSPORT environment variables.

The example script then loads a public certificate and associated private key from two files in a /security subdirectory.

var publicCert = fs.readFileSync('./security/server-cert.pem', 'utf-8');
var privateKey = fs.readFileSync('./security/server-pvk.pem', 'utf-8');

These are used not only for the HTTPS server, but also to sign requests sent to the UW IdP. You can use openssl to generate keys and certificate signing requests. The UW IdP seems to require that your server responds to HTTPS requests, so you should get a signed certificate for your server before trying to register it.

The script continues by creating a typical Express application and registering the typical middleware. For more information on this, see the Passport.js site.

Then the script creates the UW Shibboleth Strategy, and tells Passport to use it.

//create the UW Shibboleth Strategy and tell Passport to use it
var strategy = new uwshib.Strategy({
    entityId: domain,
    privateKey: privateKey,
    callbackUrl: loginCallbackUrl,
    domain: domain
});

passport.use(strategy);

In addition to the properties shown above, you may also pass any configuration properties accepted by the passport-saml library.

Note: When the UW IdP sends back Shibboleth assertions, they contain timestamps that declare when and for how long those assertions are valid. The passport-saml library will compare these timestamps against your server's clock, and will not allow any time skewing by default. If your server's clock is not synchronized with the UW IdP server, you may want to add the acceptedClockSkewMs property to the object you pass to the uwshib.Strategy() constructor. This property is defined and interpreted by the passport-saml library, and may be set to a number of milliseconds that the clocks are allowed to be off from one another. If you don't want any timestamp checking at all, you may set this property to -1. See the passport-saml configuration properties for more details.

The name of the strategy is 'uwsaml', but you can use the .name property of the Strategy to refer to that.

You will typically want to use sessions to allow users to authenticate only once per-sesion. The next functions are called by Passport to serialize and deserialize the user to the session. As noted in the comments, you would typically want to serialize only the unique ID (.netID) and reconstitute the user from your database during deserialzie. But to keep things simple, the script serializes the entire user and deserializes it again.

passport.serializeUser(function(user, done){
    done(null, user);
});

passport.deserializeUser(function(user, done){
    done(null, user);
});

Next, the script registers a few routes to handle login, the login callback, and the standard metadata. This module provides implementations for the metadata route, and you use passport.authenticate for the login and login callback routes. The login route will redirect the user to the UW single sign-on page, and the UW IdP will then redirect the user back to the login callback route.

app.get(loginUrl, passport.authenticate(strategy.name), uwshib.backToUrl());
app.post(loginCallbackUrl, passport.authenticate(strategy.name), uwshib.backToUrl());
app.get(uwshib.urls.metadata, uwshib.metadataRoute(strategy, publicCert));

The uwshib.backToUrl() is a convenience middleware that will redirect the browser back to the URL that was originally requested before authentication.

Lastly, the script tells Express to use the ensureAuth() middleware provided by this module to secure all routes declared after this.

//secure all routes following this
app.use(uwshib.ensureAuth(loginUrl));

Any route requested after this middleware will require authentication. When requested, those routes will automatically redirect to the loginUrl if the user has not already authenticated. After successful authentication, the browser will be redirected back to the original URL, and the user information will be available via the .user property on the request object.

Note that ensureAuth can also be used to selectively secure routes. For example:

app.get('protected/resource', ensureAuth(loginUrl), function(req, res) {
    //user has authenticated, do normal route processing
    //user is available via req.user
});
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