Trim spaces from admin token during authentication and validate that the admin panel token is not empty

src/config.rs

@@ -317,6 +317,12 @@ make_config! {
 }
 
 fn validate_config(cfg: &ConfigItems) -> Result<(), Error> {
+    if let Some(ref token) = cfg.admin_token {
+        if token.trim().is_empty() {
+            err!("`ADMIN_TOKEN` is enabled but has an empty value. To enable the admin page without token, use `DISABLE_ADMIN_TOKEN`")
+        }
+    }
+
     if cfg.yubico_client_id.is_some() != cfg.yubico_secret_key.is_some() {
         err!("Both `YUBICO_CLIENT_ID` and `YUBICO_SECRET_KEY` need to be set for Yubikey OTP support")
     }