implement https_only flag

src/unit.rs

@@ -348,6 +348,11 @@ fn connect_socket(unit: &Unit, hostname: &str, use_pooled: bool) -> Result<(Stre
         "http" | "https" | "test" => (),
         scheme => return Err(ErrorKind::UnknownScheme.msg(format!("unknown scheme '{}'", scheme))),
     };
+    if unit.url.scheme() != "https" && unit.agent.config.https_only {
+        return Err(ErrorKind::InsecureRequestHttpsOnly.msg(format!(
+            "can't perform non https request with https_only set"
+        )));
+    }
     if use_pooled {
         let pool = &unit.agent.state.pool;
         let proxy = &unit.agent.config.proxy;