Add token refresh function to auth utilities

src/auth/index.js

@@ -1 +1 @@
-export { login } from "./utilities";
+export { login, refresh } from "./utilities";

src/auth/utilities.js

@@ -31,3 +31,29 @@ export async function login(username, password){
 	return data.access_token || false;
 }
 
+/**
+ * Refresh current access token.
+ * @example
+ * refresh("csrf_refresh_token")
+ * @param {String} csrf_refresh_token The current CSRF validation string.
+ * @returns {Boolean | String} An access token on success, `false` otherwise.
+ */
+export async function refresh(csrf_refresh_token){
+	const refreshInit = {
+		method: "POST",
+		headers: {'X-CSRF-TOKEN': csrf_refresh_token},
+	};
+
+	let refreshResponse = await fetch("/tokens/refresh", refreshInit);
+    let data = await refreshResponse.json();
+
+    if (data === null){
+        return false;
+    }
+	if (!refreshResponse.ok){
+		console.error(`Refresh failed. Got code ${refreshResponse.status} (${refreshResponse.statusText})`);
+		return false;
+	}
+
+	return data.access_token || false;
+}