Example for device code flow added (#1328)

sdk/identity/examples/device_code_flow.rs

@@ -0,0 +1,42 @@
+use azure_core::new_http_client;
+use azure_identity::device_code_flow::start;
+use futures::{future::ready, StreamExt};
+use oauth2::ClientId;
+use std::{env, error::Error};
+
+const SCOPES: &[&str; 2] = &[".default", "offline_access"];
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    let tenant_id = env::var("TENANT_ID").expect("Missing TENANT_ID environment variable.");
+    let client_id =
+        ClientId::new(env::var("CLIENT_ID").expect("Missing CLIENT_ID environment variable."));
+
+    let client = new_http_client();
+
+    match start(client.clone(), tenant_id, client_id.as_str(), SCOPES).await {
+        Ok(response) => {
+            println!("{:?}", response.message());
+
+            response
+                .stream()
+                .for_each(|result| {
+                    match result {
+                        Ok(value) => {
+                            println!("access token: {:?}", value.access_token().secret());
+                            match value.refresh_token() {
+                                None => {}
+                                Some(tk) => println!("refresh token: {:?}", tk.secret()),
+                            }
+                        }
+                        Err(_) => println!("waiting..."),
+                    }
+                    ready(())
+                })
+                .await
+        }
+        Err(err) => println!("error: {:?}", err),
+    }
+
+    Ok(())
+}