Cannot access the user-object in tRPC createContext (express)

I'm having an issue where my tRPC-configuration cannot access the express session on the request object.

I am using passport.js with google and facebook providers, and on any normal http-route (not on the tRPC router), I get the userinfo when calling req.user.

app.ts:

import * as trpc from '@trpc/server';
import * as trpcExpress from '@trpc/server/adapters/express';

const appRouter = trpc
    .router()
    .mutation('addTodo', {
        input: z.string(),
        resolve: ({input, ctx}) => {
            // Add a todo
        },
    });

const app = express();
app.use(
    session({
        secret: 'use an env-variable here',
    }),
);
app.use(passport.initialize());
app.use(passport.session());

app.use(
    '/trpc',
    trpcExpress.createExpressMiddleware({
        router: appRouter,
        createContext: (ctx: trpcExpress.CreateExpressContextOptions) => {
            // === HERE LIES THE ISSUE ===
            console.log(ctx.req.user);
            //                   ^ THIS RETURNS UNDEFINED
            return ctx;
        },
    }),
);

app.get("ping", (req, res) => {
    console.log(req.user);
    //                ^ THIS RETURNS THE USER
    res.send("pong");
})

It would be easy to say that tRPC doesn't support give you the user, but there must be some sort of workaround, right?

I added this to my client-side fetcher used by trpc

{
  credentials: "include"
}