fix(loki sink): Send auth header for healchecks (#4604)

Fixes #3710

Signed-off-by: Jesse Szwedko <jesse@szwedko.me>

src/sinks/loki.rs

@@ -196,7 +196,11 @@ impl HttpSink for LokiConfig {
 async fn healthcheck(config: LokiConfig, mut client: HttpClient) -> crate::Result<()> {
     let uri = format!("{}ready", config.endpoint);
 
-    let req = http::Request::get(uri).body(hyper::Body::empty()).unwrap();
+    let mut req = http::Request::get(uri).body(hyper::Body::empty()).unwrap();
+
+    if let Some(auth) = &config.auth {
+        auth.apply(&mut req);
+    }
 
     let res = client.send(req).await?;
 
@@ -211,8 +215,10 @@ async fn healthcheck(config: LokiConfig, mut client: HttpClient) -> crate::Resul
 mod tests {
     use super::*;
     use crate::sinks::util::http::HttpSink;
-    use crate::sinks::util::test::load_sink;
+    use crate::sinks::util::test::{build_test_server, load_sink};
+    use crate::test_util;
     use crate::Event;
+    use futures::StreamExt;
 
     #[test]
     fn interpolate_labels() {
@@ -277,6 +283,46 @@ mod tests {
 
         assert_eq!(record.labels[0], ("bar".to_string(), "bar".to_string()));
     }
+
+    #[tokio::test]
+    async fn healthcheck_includes_auth() {
+        let (mut config, cx) = load_sink::<LokiConfig>(
+            r#"
+            endpoint = "http://localhost:3100"
+            labels = {test_name = "placeholder"}
+			auth.strategy = "basic"
+			auth.user = "username"
+			auth.password = "some_password"
+        "#,
+        )
+        .unwrap();
+
+        let addr = test_util::next_addr();
+        let endpoint = format!("http://{}", addr);
+        config.endpoint = endpoint
+            .clone()
+            .parse::<http::Uri>()
+            .expect("could not create URI")
+            .into();
+
+        let (rx, _trigger, server) = build_test_server(addr);
+        tokio::spawn(server);
+
+        let tls = TlsSettings::from_options(&config.tls).expect("could not create TLS settings");
+        let client = HttpClient::new(cx.resolver(), tls).expect("could not cerate HTTP client");
+
+        healthcheck(config.clone(), client)
+            .await
+            .expect("healthcheck failed");
+
+        let output = rx.take(1).collect::<Vec<_>>().await;
+        assert_eq!(
+            Some(&http::header::HeaderValue::from_static(
+                "Basic dXNlcm5hbWU6c29tZV9wYXNzd29yZA=="
+            )),
+            output[0].0.headers.get("authorization")
+        );
+    }
 }
 
 #[cfg(feature = "loki-integration-tests")]