Allow overriding server name

src/connector.rs

@@ -21,6 +21,7 @@ pub struct HttpsConnector<T> {
     force_https: bool,
     http: T,
     tls_config: Arc<rustls::ClientConfig>,
+    override_server_name: Option<String>,
 }
 
 impl<T> fmt::Debug for HttpsConnector<T> {
@@ -40,6 +41,7 @@ where
             force_https: false,
             http,
             tls_config: cfg.into(),
+            override_server_name: None,
         }
     }
 }
@@ -83,21 +85,26 @@ where
                 Box::pin(f)
             } else if sch == &http::uri::Scheme::HTTPS {
                 let cfg = self.tls_config.clone();
-                let hostname = dst
-                    .host()
-                    .unwrap_or_default()
-                    .to_string();
+                let hostname = match self.override_server_name.as_deref() {
+                    Some(h) => h,
+                    None => dst.host().unwrap_or_default(),
+                };
+                let hostname = match rustls::ServerName::try_from(hostname) {
+                    Ok(dnsname) => dnsname,
+                    Err(_) => {
+                        let err = io::Error::new(io::ErrorKind::Other, "invalid dnsname");
+                        return Box::pin(async move { Err(Box::new(err).into()) });
+                    }
+                };
                 let connecting_future = self.http.call(dst);
 
                 let f = async move {
                     let tcp = connecting_future
                         .await
                         .map_err(Into::into)?;
                     let connector = TlsConnector::from(cfg);
-                    let dnsname = rustls::ServerName::try_from(hostname.as_str())
-                        .map_err(|_| io::Error::new(io::ErrorKind::Other, "invalid dnsname"))?;
                     let tls = connector
-                        .connect(dnsname, tcp)
+                        .connect(hostname, tcp)
                         .await
                         .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
                     Ok(MaybeHttpsStream::Https(tls))

src/connector/builder.rs

@@ -106,6 +106,7 @@ impl ConnectorBuilder<WantsSchemes> {
         ConnectorBuilder(WantsProtocols1 {
             tls_config: self.0.tls_config,
             https_only: true,
+            override_server_name: None,
         })
     }
 
@@ -117,6 +118,7 @@ impl ConnectorBuilder<WantsSchemes> {
         ConnectorBuilder(WantsProtocols1 {
             tls_config: self.0.tls_config,
             https_only: false,
+            override_server_name: None,
         })
     }
 }
@@ -128,6 +130,7 @@ impl ConnectorBuilder<WantsSchemes> {
 pub struct WantsProtocols1 {
     tls_config: ClientConfig,
     https_only: bool,
+    override_server_name: Option<String>,
 }
 
 impl WantsProtocols1 {
@@ -136,6 +139,7 @@ impl WantsProtocols1 {
             force_https: self.https_only,
             http: conn,
             tls_config: std::sync::Arc::new(self.tls_config),
+            override_server_name: self.override_server_name,
         }
     }
 
@@ -169,6 +173,20 @@ impl ConnectorBuilder<WantsProtocols1> {
             enable_http1: false,
         })
     }
+
+    /// Override server name for the TLS stack
+    ///
+    /// By default, for each connection hyper-rustls will extract host portion
+    /// of the destination URL and verify that server certificate contains
+    /// this value.
+    ///
+    /// If this method is called, hyper-rustls will instead verify that server
+    /// certificate contains `override_server_name`. Domain name included in
+    /// the URL will not affect certificate validation.
+    pub fn with_server_name(mut self, override_server_name: String) -> Self {
+        self.0.override_server_name = Some(override_server_name);
+        self
+    }
 }
 
 /// State of a builder with HTTP1 enabled, that may have some other