Implement an ability to work without default client

examples/custom_client.rs

@@ -0,0 +1,43 @@
+//! This example demonstrates how to use the same connection pool for both obtaining the tokens and
+//! using the API that these tokens authorize. In most cases e.g. obtaining the service account key
+//! will already establish a keep-alive http connection, so the succeeding API call should be much
+//! faster.
+//!
+//! It is also a better use of resources (memory, sockets, etc.)
+
+async fn r#use<C>(
+    client: hyper::Client<C>,
+    authenticator: yup_oauth2::authenticator::Authenticator<C>,
+) -> Result<(), Box<dyn std::error::Error + Send + Sync>>
+where
+    C: Clone + Send + Sync + hyper::client::connect::Connect + 'static,
+{
+    let token = authenticator.token(&["email"]).await?;
+    let request = http::Request::get("https://example.com")
+        .header(
+            http::header::AUTHORIZATION,
+            format!("Bearer {}", token.as_str()),
+        )
+        .body(hyper::body::Body::empty())?;
+    let response = client.request(request).await?;
+    drop(response); // Implementing handling of the response is left as an exercise for the reader.
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() {
+    let google_credentials = std::env::var("GOOGLE_APPLICATION_CREDENTIALS")
+        .expect("env var GOOGLE_APPLICATION_CREDENTIALS is required");
+    let secret = yup_oauth2::read_service_account_key(google_credentials)
+        .await
+        .expect("$GOOGLE_APPLICATION_CREDENTIALS is not a valid service account key");
+    let client = hyper::Client::builder().build(hyper_rustls::HttpsConnector::with_native_roots());
+    let authenticator =
+        yup_oauth2::ServiceAccountAuthenticator::with_client(secret, client.clone())
+            .build()
+            .await
+            .expect("could not create an authenticator");
+    r#use(client, authenticator)
+        .await
+        .expect("use is successful!");
+}