CXX-572 Backport server r3.0.1..r3.0.2 changes

Server SHAs cherry-picked into this commit:

6fa5d19
d9a3c65

Author: acmorrow

src/mongo/bson/bsonelement.cpp

@@ -740,6 +740,13 @@ namespace mongo {
         return true;
     }
 
+    template<> bool BSONElement::coerce<long long>( long long* out ) const {
+        if ( !isNumber() )
+            return false;
+        *out = numberLong();
+        return true;
+    }
+
     template<> bool BSONElement::coerce<double>( double* out ) const {
         if ( !isNumber() )
             return false;

src/mongo/client/sasl_client_authenticate_impl.cpp

@@ -159,7 +159,8 @@ namespace {
         if (status.isOK()) {
             session->setParameter(SaslClientSession::parameterPassword, value);
         }
-        else if (status != ErrorCodes::NoSuchKey) {
+        else if (!(status == ErrorCodes::NoSuchKey && targetDatabase == "$external")) {
+            // $external users do not have passwords, hence NoSuchKey is expected
             return status;
         }
 

src/mongo/client/sasl_scramsha1_client_conversation.cpp

@@ -78,6 +78,10 @@ namespace mongo {
      * n,a=authzid,n=encoded-username,r=client-nonce
      */
     StatusWith<bool> SaslSCRAMSHA1ClientConversation::_firstStep(std::string* outputData) {
+        if (_saslClientSession->getParameter(SaslClientSession::parameterPassword).empty()) {
+            return StatusWith<bool>(ErrorCodes::BadValue, mongoutils::str::stream() <<
+                                    "Empty client password provided");
+        }
 
         // Create text-based nonce as base64 encoding of a binary blob of length multiple of 3
         const int nonceLenQWords = 3;