Pull all required headers to be signed.

Fixes scality/cloudserver#120

lib/auth/auth.js

@@ -98,7 +98,6 @@ auth.generateV4Headers =
         const amzDate = convertUTCtoISO8601(Date.now());
         // get date without time
         const scopeDate = amzDate.slice(0, amzDate.indexOf('T'));
-        const signedHeaders = 'host;x-amz-date;x-amz-content-sha256';
         const region = 'us-east-1';
         const service = awsService || 'iam';
         const credentialScope =
@@ -117,11 +116,12 @@ auth.generateV4Headers =
         request.setHeader('host', request._headers.host);
         request.setHeader('x-amz-date', amzDate);
         request.setHeader('x-amz-content-sha256', payloadChecksum);
-        Object.assign(request.headers, { host: request.getHeader('host') });
-        Object.assign(request.headers, { 'x-amz-date': amzDate });
-        Object.assign(request.headers,
-                      { 'x-amz-content-sha256': payloadChecksum });
-
+        Object.assign(request.headers, request._headers);
+        const signedHeaders = Object.keys(request._headers)
+            .filter(headerName =>
+            headerName.startsWith('x-amz-') || headerName.startsWith('x-scal-')
+              || headerName === 'host'
+        ).sort().join(';');
         const params = { request, signedHeaders, payloadChecksum,
                          credentialScope, timestamp, query: data,
                          awsService: service };