https://github.com/rustls/rustls-native-certs/issues/28
https://github.com/rustls/rustls-native-certs/commit/8162b232045e

--- cargo-crates/rustls-native-certs-0.7.0/src/unix.rs.orig	1970-01-01 00:00:00 UTC
+++ cargo-crates/rustls-native-certs-0.7.0/src/unix.rs
@@ -2,13 +2,27 @@ use pki_types::CertificateDer;
 
 use pki_types::CertificateDer;
 
+use std::fs;
 use std::io::Error;
 
 pub fn load_native_certs() -> Result<Vec<CertificateDer<'static>>, Error> {
     let likely_locations = openssl_probe::probe();
 
-    match likely_locations.cert_file {
-        Some(cert_file) => load_pem_certs(&cert_file),
-        None => Ok(Vec::new()),
+    let mut certs = match likely_locations.cert_file {
+        Some(cert_file) => load_pem_certs(&cert_file)?,
+        None => Vec::new(),
+    };
+
+    if let Some(cert_dir) = likely_locations.cert_dir {
+        let dir_reader = fs::read_dir(cert_dir)?;
+        for entry in dir_reader {
+            let entry = entry?;
+            let path = entry.path();
+            if fs::metadata(&path)?.is_file() {
+                certs.append(&mut load_pem_certs(&path)?);
+            }
+        }
     }
+
+    Ok(certs)
 }
