Passport "Hello World" always fails

I have the following:

import {Router} from 'express';
import passport from 'passport';
import {Strategy} from 'passport-local';
import pg from 'pg';
import {pgUri} from '../environment';

let loginRouter = Router();

passport.use(new Strategy((username, password, done) => done(null, true)));
//{
//    pg.connectAsync(pgUri)
//        .then(([client, release]) => {
//            return client.queryAsync('select * from users where "user" = $1::TEXT', [username])
//                .finally(release);
//        })
//        .tap(result => console.log(result.rows))
//        .then(result => done(null, true));
//}));

loginRouter.get('/', (request, response) => response.render('login'));
loginRouter.post('/', passport.authenticate('local', {successRedirect: '/',
                                                      failureRedirect: '/login'}));

It's an express route file that defines the simplest possible authentication scheme. The above always redirects back to /login, indicating a failure.

What I've tried

• Changing failureRedirect to /loginFailed really redirects there. So the login does fail.
• Breakpoints and console.logs inside the function body do not get hit.
• Calling done with done(null, {foo: "bar"}) instead of true changes nothing.

Worth noting

• I'm using babel for ES6 support, but since this is the only part failing, and the breakpoints I can set (before passport.use) show expected values for all variables, I don't think that's the problem.
• The .get() route works as expected, displaying the form.

Here's the form I'm using (directly copied from the passport example

<form action="/login" method="post">
    <div>
        <label>Username:</label>
        <input type="text" name="username"/>
    </div>
    <div>
        <label>Password:</label>
        <input type="password" name="password"/>
    </div>
    <div>
        <input type="submit" value="Log In"/>
    </div>
</form>

I have no idea what went wrong here. Would appreciate any help.