Allow setting the additionalParams in .authenticate

I need to send in the RelayState when asking to login. This relay state is different for each user so I need it to be set when the user requests /login (and then .authenticate()) as opposed to when I start my server and setup passport.use(.

Basically I would like to:

  app.get('/login',
    passport.authenticate(config.passport.strategy,
      {
        additionalParams: {'RelayState': req.url},
        failureRedirect: '/loginFail'
      })
  );

Obviously even the above wouldn’t work since I don’t have access to the req variable. Perhaps there’s a better way to simply have the user return to the page they were asking for.

[jylauril]

Pro tip: You can wrap the passport.auhenticate call inside your own middleware function so you can access the request and response if needed:

  app.get('/login', function(req, res, next) {
    passport.authenticate(config.passport.strategy,
      {
        additionalParams: {'RelayState': req.url},
        failureRedirect: '/loginFail'
      })(req, res, next); // <- just remember to add these
  });

[blackpuppy]

I got the same problem, that is, not able to pass additionalParams in the second argument to passport.authenticate(). And eventually found the following solution. Note that I am using TypeScript.

// need to use AuthenticateOptions from passport-saml
import { AuthenticateOptions } from "passport-saml/lib/passport-saml/types";

// then for GET /login route
const relayState = "your-state";  // like a key of the intended URL in a cache
const options: AuthenticateOptions = {
    failureRedirect: "/",
    additionalParams: {
        RelayState: relayState,
    },
};
passport.authenticate("saml", options)(req, res);

// later in POST /login/callback
const relayState = req.body.RelayState;
const redirectUrl = MyCache.get(relayState);
res.redirect(redirectUrl);

TypeScript checks the 2nd argument against the AuthenticateOptions defined in passport, and it does not have additionalParams, so there is a type error. Using the AuthenticateOptions defined in passport-saml solves it. But for JavaScript, it does not have this type checking. So I think it should just work.