Add a basic casbin example for actix-web. (#264)

* Add the casbin example for actix-web.

* Update for clear description.

casbin/src/main.rs

@@ -0,0 +1,58 @@
+use casbin::{DefaultModel, Enforcer, FileAdapter, RbacApi};
+use std::boxed::Box;
+use std::io;
+use std::sync::RwLock;
+
+use actix_web::{middleware, web, App, HttpRequest, HttpResponse, HttpServer};
+
+/// simple handle
+async fn success(
+    enforcer: web::Data<RwLock<Enforcer>>,
+    req: HttpRequest,
+) -> HttpResponse {
+    let mut e = enforcer.write().unwrap();
+    println!("{:?}", req);
+    assert_eq!(vec!["data2_admin"], e.get_roles_for_user("alice", None));
+
+    HttpResponse::Ok().body("Success: alice is data2_admin.")
+}
+
+async fn fail(enforcer: web::Data<RwLock<Enforcer>>, req: HttpRequest) -> HttpResponse {
+    let mut e = enforcer.write().unwrap();
+    println!("{:?}", req);
+    assert_eq!(vec!["data1_admin"], e.get_roles_for_user("alice", None));
+
+    HttpResponse::Ok().body("Fail: alice is not data1_admin.") // In fact, it can't be displayed.
+}
+
+#[actix_rt::main]
+async fn main() -> io::Result<()> {
+    std::env::set_var("RUST_LOG", "info");
+    std::env::set_var("LOGE_FORMAT", "target");
+
+    loge::init();
+
+    let model = DefaultModel::from_file("rbac/rbac_model.conf")
+        .await
+        .unwrap();
+    let adapter = FileAdapter::new("rbac/rbac_policy.csv");
+
+    let e = Enforcer::new(Box::new(model), Box::new(adapter))
+        .await
+        .unwrap();
+    let e = web::Data::new(RwLock::new(e)); // wrap enforcer into actix-state
+
+    //move is necessary to give closure below ownership of counter
+    HttpServer::new(move || {
+        App::new()
+            .app_data(e.clone()) // <- create app with shared state
+            // enable logger
+            .wrap(middleware::Logger::default())
+            // register simple handler, handle all methods
+            .service(web::resource("/success").to(success))
+            .service(web::resource("/fail").to(fail))
+    })
+    .bind("127.0.0.1:8080")?
+    .run()
+    .await
+}