Improve proxy authentication preventing NPE and allow Basic Authentication (v3)

core/src/main/scalajvm/sttp/client3/HttpClientAsyncBackend.scala

@@ -54,7 +54,12 @@ abstract class HttpClientAsyncBackend[F[_], S, P, BH, B](
 
         val consumer = toJavaBiConsumer((t: HttpResponse[BH], u: Throwable) => {
           if (t != null) {
-            try success(readResponse(t, Left(bodyHandlerBodyToBody(t.body())), request))
+            // sometimes body returned by HttpClient can be null, we handle this by returning empty body to prevent NPE
+            val body = Option(t.body())
+              .map(bodyHandlerBodyToBody)
+              .getOrElse(emptyBody())
+
+            try success(readResponse(t, Left(body), request))
             catch {
               case e: Exception => error(e)
             }

core/src/main/scalajvm/sttp/client3/HttpClientBackend.scala

@@ -10,6 +10,7 @@ import sttp.monad.MonadError
 import sttp.monad.syntax._
 import sttp.ws.WebSocket
 
+import java.net.Authenticator.RequestorType
 import java.net.http.{HttpClient, HttpRequest, HttpResponse}
 import java.net.{Authenticator, PasswordAuthentication}
 import java.time.{Duration => JDuration}
@@ -123,10 +124,12 @@ abstract class HttpClientBackend[F[_], S, P, B](
 object HttpClientBackend {
 
   type EncodingHandler[B] = PartialFunction[(B, String), B]
-  // TODO not sure if it works
+
   private class ProxyAuthenticator(auth: SttpBackendOptions.ProxyAuth) extends Authenticator {
     override def getPasswordAuthentication: PasswordAuthentication = {
-      new PasswordAuthentication(auth.username, auth.password.toCharArray)
+      if (getRequestorType == RequestorType.PROXY) {
+        new PasswordAuthentication(auth.username, auth.password.toCharArray)
+      } else null
     }
   }
 

docs/conf/proxy.md

@@ -31,6 +31,16 @@ import sttp.client3._
 SttpBackendOptions.httpProxy("some.host", 8080, "username", "password")
 ```
 
+If your backend implements `HttpClientBackend` and your proxy server requires Basic authentication, you will need to enable it by 
+removing Basic from the `jdk.http.auth.tunneling.disabledSchemes` networking property, or by setting a system property of the same name to "".
+
+```scala mdoc:compile-only 
+System.setProperty("jdk.http.auth.tunneling.disabledSchemes", "")
+```
+
+Please be aware that enabling Basic authentication for HTTP tunneling can expose your credentials to interception, so it
+should only be done if you understand the risks and your network is secure. This behaviour is described in https://www.oracle.com/java/technologies/javase/8u111-relnotes.html.
+
 ## Ignoring and allowing specific hosts
 
 There are two additional settings that can be provided to via `SttpBackendOptions`: