Add SSL support (#7)

Fixes #1

nut-client/src/ssl/mod.rs

@@ -0,0 +1,40 @@
+use crate::Config;
+
+/// The certificate validation mechanism for NUT.
+pub struct NutCertificateValidator {
+    debug: bool,
+}
+
+impl NutCertificateValidator {
+    /// Initialize a new instance.
+    pub fn new(config: &Config) -> Self {
+        NutCertificateValidator {
+            debug: config.debug,
+        }
+    }
+}
+
+impl rustls::ServerCertVerifier for NutCertificateValidator {
+    fn verify_server_cert(
+        &self,
+        _roots: &rustls::RootCertStore,
+        presented_certs: &[rustls::Certificate],
+        _dns_name: webpki::DNSNameRef<'_>,
+        _ocsp: &[u8],
+    ) -> Result<rustls::ServerCertVerified, rustls::TLSError> {
+        // todo: verify certificates, but not hostnames
+
+        if self.debug {
+            let parsed = webpki::EndEntityCert::from(presented_certs[0].0.as_slice()).ok();
+            if let Some(_parsed) = parsed {
+                eprintln!("DEBUG <- Certificate received and parsed");
+                // todo: reading values here... https://github.com/briansmith/webpki/pull/103
+            } else {
+                eprintln!("DEBUG <- Certificate not-parseable");
+            }
+        }
+
+        // trust everything for now
+        Ok(rustls::ServerCertVerified::assertion())
+    }
+}