Other methods allow users to sign in to a microservice with the provided credentials. Look at the following signin function that processes requests that are sent to the /signin path:

fn signin((req, params): (HttpRequest<State>, Form<UserForm>))
    -> FutureResponse<HttpResponse>
{
    let fut = post_request("http://127.0.0.1:8001/signin", params.into_inner())
        .map(move |id: UserId| {
            req.remember(id.id);
            HttpResponse::build_from(&req)
            .status(StatusCode::FOUND)
            .header(header::LOCATION, "/comments.html")
            .finish()
        });
    Box::new(fut)
}

The function has two parameters: HttpRequest and Form. The first we need to get access to a shared State object. The second we need to extract the UserForm struct from the request body. We can also use the post_request function here, but expect it to return a UserId value in its response. The UserId struct is declared as follows:

#[derive(Deserialize)]
pub struct UserId {
    id: String,
}

Since HttpRequest implements the RequestIdentity trait and we plugged in  IdentityService to App, we can call the remember method with a user's ID to associate the current session with a user.

After this, we create a response with the 302 status code, as we did in the previous handler, and redirect users to  the /comments.html page. But we have to build an HttpResponse instance from HttpRequest to keep the changes of the remember function call.