Make `get_or_error` generic

Thanks to Andreu Botella!

src/config.rs

@@ -15,9 +15,6 @@
 
 use serde::de::Deserialize;
 
-use pamsm::PamError;
-use libnss::interop::Response;
-
 extern crate config;
 
 const DEFAULT_CONFIG_FILE: &str = "/etc/nss_pam_oidc";
@@ -73,12 +70,7 @@ pub fn get_optional<'de, T: Deserialize<'de>>(conf: &config::Config, key: &str)
     }
 }
 
-enum DesiredError {
-    Response,
-    PamError
-}
-
-pub fn get_or_error<'de, T: Deserialize<'de>>(config: &config::Config, key: &str, error_value: DesiredError) -> Result<T, Response> {
+pub fn get_or_error<'de, T: Deserialize<'de>, E>(config: &config::Config, key: &str, error_value: E) -> Result<T, E> {
     match get_optional(config, key) {
         Some(v) => {
             debug!("Configuration key found: {}", key);