Allow TLS client config to be overridden

See: https://docs.rs/rustls/latest/rustls/struct.ClientConfig.html

src/request.rs

@@ -1,5 +1,7 @@
 use std::io::Read;
 use std::sync::{Arc, Mutex};
+#[cfg(feature = "tls")]
+use std::fmt;
 
 use lazy_static::lazy_static;
 use qstring::QString;
@@ -46,6 +48,8 @@ pub struct Request {
     pub(crate) timeout_write: u64,
     pub(crate) redirects: u32,
     pub(crate) proxy: Option<crate::proxy::Proxy>,
+    #[cfg(feature = "tls")]
+    pub(crate) tls_config: Option<TLSClientConfig>,
 }
 
 impl ::std::fmt::Debug for Request {
@@ -554,4 +558,31 @@ impl Request {
         self.proxy = Some(proxy);
         self
     }
+
+    /// Set the TLS client config to use for the connection.
+    ///
+    /// See [`ClientConfig`](https://docs.rs/rustls/latest/rustls/struct.ClientConfig.html).
+    ///
+    /// Example:
+    /// ```
+    /// let tls_config = std::sync::Arc::new(rustls::ClientConfig::new());
+    /// let req = ureq::post("https://cool.server")
+    ///     .set_tls_config(tls_config.clone());
+    /// ```
+    #[cfg(feature = "tls")]
+    pub fn set_tls_config(&mut self, tls_config: Arc<rustls::ClientConfig>) -> &mut Request {
+        self.tls_config = Some(TLSClientConfig(tls_config));
+        self
+    }
+}
+
+#[cfg(feature = "tls")]
+#[derive(Clone)]
+pub(crate) struct TLSClientConfig(pub(crate) Arc<rustls::ClientConfig>);
+
+#[cfg(feature = "tls")]
+impl fmt::Debug for TLSClientConfig {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TLSClientConfig").finish()
+    }
 }