+str #22345 #21854 provide forward compatible TLS constructor in stream TLS

This method will be consumed mainly by akka-http.

(cherry picked from commit 7b7a82c1c13dce5710c6cc2923fc7490666d8c79)

akka-stream/src/main/scala/akka/stream/scaladsl/TLS.scala

@@ -167,6 +167,20 @@ object TLS {
     closing:         TLSClosing
   ): scaladsl.BidiFlow[SslTlsOutbound, ByteString, ByteString, SslTlsInbound, NotUsed] =
     new scaladsl.BidiFlow(TlsModule(Attributes.none, _ ⇒ createSSLEngine(), (_, session) ⇒ verifySession(session), closing))
+
+  /**
+   * Create a StreamTls [[akka.stream.scaladsl.BidiFlow]]. This is a low-level interface.
+   *
+   * You can specify a constructor to create an SSLEngine that must already be configured for
+   * client and server mode and with all the parameters for the first session.
+   *
+   * For a description of the `closing` parameter please refer to [[TLSClosing]].
+   */
+  def apply(
+    createSSLEngine: () ⇒ SSLEngine, // we don't offer the internal `ActorSystem => SSLEngine` API here, see #21753
+    closing:         TLSClosing
+  ): scaladsl.BidiFlow[SslTlsOutbound, ByteString, ByteString, SslTlsInbound, NotUsed] =
+    apply(createSSLEngine, _ ⇒ Success(()), closing)
 }
 
 /**