How to await setting cookies when using supabase with tRPC?

[benfah]

Hi everybody,
I'm currently facing issues with my tRPC and supabase setup.

This is my function which supplies a supabase client to my tRPC context based on the resHeaders and the request tRPC provides when creating a context:

export async function createTRPCSupabaseClient(
  trpcOptions: FetchCreateContextFnOptions
) {
  return createServerClient(
    process.env.NEXT_PUBLIC_SUPABASE_URL!,
    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
    {
      cookies: {
        getAll() {
          return getCookies(trpcOptions.req);
        },
        setAll(cookiesToSet) {
          try {
            cookiesToSet.forEach(({ name, value, options }) => {
              setCookie(trpcOptions.resHeaders, name, value, options);
            });
          } catch {
            // The `setAll` method was called from a Server Component.
            // This can be ignored if you have middleware refreshing
            // user sessions.
          }
        },
      },
    }
  );
}

And this is my WIP login tRPC procedure:

export const authRouter = createTRPCRouter({
  login: publicProcedure.input(loginSchema).mutation(async ({ ctx, input }) => {
    const client = ctx.supabase;
    const { error, data } = await client.auth.signInWithPassword({
      email: input.email,
      password: input.password,
    });
    if (error)
      throw new TRPCError({
        code: "UNAUTHORIZED",
        cause: error,
        message: "Not authorized.",
      });
  }),
});

Now my issue is that the tRPC request is already done and the response is already sent to the server before supabase can set the auth headers. So how can I await that supabase sets the cookies before tRPC responds to the client?

Thanks!