How do I set a context dynamically?

Question

I don't fully understand middleware in trpc and especially using it for adminProcedures.

So my trpc.ts looks like this:

import { UserRoles } from '@/pages/api/enums';
import { UserDocument } from '@/pages/api/schemas/user_schema';
import { TRPCError, initTRPC } from '@trpc/server';

interface Context {
    user?: UserDocument
}
const t = initTRPC.context().create();

export const middleware = t.middleware;
export const router = t.router;
export const publicProcedure = t.procedure;

const isAdmin = middleware(async (opts) = {

const { ctx } = opts;

if (!ctx.user?.roles.includes(UserRoles.ADMIN || UserRoles.SUPERADMIN)) {
        throw new TRPCError({ code: 'UNAUTHORIZED' });
    }
    return opts.next({
        ctx: {
            user: ctx.user,
        },
    });
});

export const adminProcedure = publicProcedure.use(isAdmin);

What I don't understand is how do I inject user into the context?

I get user with public procedure:
export const getUser = publicProcedure
  .input(
    z.object({
      walletAddress: z.string(),
    })
  )
  .mutation(async (opts) = {

const db = await connectDB();
    const user = await User.findOne({
      walletAddress: opts.input.walletAddress,
    });

opts.ctx.user = user ?? undefined;
    return user as UserDocument;
  });

Now I try to inject it inside the procedure but when I console log the user inside the middleware function it shows undefined.

How do I set a context dynamically?

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