[sasl] order mechanisms to prefer the most secure

The previous logic was:

- use the preferred SASL mechanism if available
- otherwise use the first supported mechanism offered by the server

However RFC 6120, section 6.3.3 states:

"The initiating entity MUST maintain its own preference order independent
of the preference order of the receiving entity."

The new logic is:

- order our supported mechanisms from most secure to least secure
- if the user sets QXmppConfiguration::saslMechanism, put it first
- use the best mechanism supported by the server

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/qxmppsasl/tst_qxmppsasl.cpp b/tests/qxmppsasl/tst_qxmppsasl.cpp
index 4d5bc5dd..1626c59f 100644
--- a/tests/qxmppsasl/tst_qxmppsasl.cpp
+++ b/tests/qxmppsasl/tst_qxmppsasl.cpp
@@ -189,7 +189,7 @@ void tst_QXmppSasl::testSuccess()
 
 void tst_QXmppSasl::testClientAvailableMechanisms()
 {
-    QCOMPARE(QXmppSaslClient::availableMechanisms(), QStringList() << "PLAIN" << "DIGEST-MD5" << "ANONYMOUS" << "SCRAM-SHA-1" << "SCRAM-SHA-256" << "X-FACEBOOK-PLATFORM" << "X-MESSENGER-OAUTH2" << "X-OAUTH2");
+    QCOMPARE(QXmppSaslClient::availableMechanisms(), QStringList() << "SCRAM-SHA-256" << "SCRAM-SHA-1" << "DIGEST-MD5" << "PLAIN" << "ANONYMOUS" << "X-FACEBOOK-PLATFORM" << "X-MESSENGER-OAUTH2" << "X-OAUTH2");
 }
 
 void tst_QXmppSasl::testClientBadMechanism()