Write code to get auth key

cli/src/main.rs

@@ -1,3 +1,9 @@
-fn main() {
+use std::env;
-    println!("Hello, world!");
+
+fn get_auth_key() -> Option<String> {
+    env::var("AUTH_KEY").ok()
+}
+
+fn main() {
+    let _auth_key = get_auth_key().expect("Could not find authorization key");
 }