Rebuild actix-identity on top of actix-session (#246)

Co-authored-by: Rob Ede <robjtede@icloud.com>

actix-identity/examples/identity.rs

@@ -0,0 +1,84 @@
+//! A rudimentary example of how to set up and use `actix-identity`.
+//!
+//! ```bash
+//! # using HTTPie (https://httpie.io/cli)
+//!
+//! # outputs "Welcome Anonymous!" message
+//! http -v --session=identity GET localhost:8080/
+//!
+//! # log in using fake details, ensuring that --session is used to persist cookies
+//! http -v --session=identity POST localhost:8080/login user_id=foo
+//!
+//! # outputs "Welcome User1" message
+//! http -v --session=identity GET localhost:8080/
+//! ```
+
+use std::io;
+
+use actix_identity::{Identity, IdentityMiddleware};
+use actix_session::{storage::CookieSessionStore, SessionMiddleware};
+use actix_web::{
+    cookie::Key, get, middleware::Logger, post, App, HttpMessage, HttpRequest, HttpResponse,
+    HttpServer, Responder,
+};
+
+#[actix_web::main]
+async fn main() -> io::Result<()> {
+    env_logger::init_from_env(env_logger::Env::new().default_filter_or("info"));
+
+    let secret_key = Key::generate();
+
+    HttpServer::new(move || {
+        let session_mw =
+            SessionMiddleware::builder(CookieSessionStore::default(), secret_key.clone())
+                // disable secure cookie for local testing
+                .cookie_secure(false)
+                .build();
+
+        App::new()
+            // Install the identity framework first.
+            .wrap(IdentityMiddleware::default())
+            // The identity system is built on top of sessions. You must install the session
+            // middleware to leverage `actix-identity`. The session middleware must be mounted
+            // AFTER the identity middleware: `actix-web` invokes middleware in the OPPOSITE
+            // order of registration when it receives an incoming request.
+            .wrap(session_mw)
+            .wrap(Logger::default())
+            .service(index)
+            .service(login)
+            .service(logout)
+    })
+    .bind(("127.0.0.1", 8080))
+    .unwrap()
+    .workers(2)
+    .run()
+    .await
+}
+
+#[get("/")]
+async fn index(user: Option<Identity>) -> impl Responder {
+    if let Some(user) = user {
+        format!("Welcome! {}", user.id().unwrap())
+    } else {
+        "Welcome Anonymous!".to_owned()
+    }
+}
+
+#[post("/login")]
+async fn login(request: HttpRequest) -> impl Responder {
+    // Some kind of authentication should happen here -
+    // e.g. password-based, biometric, etc.
+    // [...]
+
+    // Attached a verified user identity to the active
+    // session.
+    Identity::login(&request.extensions(), "User1".into()).unwrap();
+
+    HttpResponse::Ok()
+}
+
+#[post("/logout")]
+async fn logout(user: Identity) -> impl Responder {
+    user.logout();
+    HttpResponse::NoContent()
+}