Author: František Dvořák <valtri@civ.zcu.cz>
Date:   Thu Mar 31 22:48:51 2016 +0200

    IMPALA-2645: set mechUsing only on success
    
    Better to check success status from sasl_client_start() before using returned structure with auth mechanism. According to the API documentation, its value is guaranteed only after success (no error or SASL_CONTINUE).

diff --git a/be/src/transport/TSasl.cpp b/be/src/transport/TSasl.cpp
index 31e1e1a..3108dff 100644
--- a/be/src/transport/TSasl.cpp
+++ b/be/src/transport/TSasl.cpp
@@ -148,7 +148,9 @@ uint8_t* TSaslClient::evaluateChallengeOrResponse(
           &outlen,   /* filled in on success */
           (const char**)&mechUsing);
     clientStarted = true;
-    chosenMech = mechUsing;
+    if (result == SASL_OK || result == SASL_CONTINUE) {
+      chosenMech = mechUsing;
+    }
   } else {
     if (len  > 0) {
       result=sasl_client_step(conn,  /* our context */