Add rpc signature handler

pkg/donut/donut-metadata.md

@@ -0,0 +1,55 @@
+##### Users Collection
+
+```js
+
+"minio": {
+    "version": 1,
+    "users": [{
+    	"secretAccessKey": String,
+    	"accessKeyId": String,
+    	"status": String // enum: ok, disabled, deleted
+    }],
+    "hosts": [{
+    	"address": String,
+    	"uuid": String,
+    	"status": String, // enum: ok, disabled, deleted, busy, offline.
+    	"disks": [{
+        		"disk": String,
+        		"uuid": String,
+        		"status": String // ok, offline, disabled, busy.
+        }]
+    }]
+}
+```
+
+##### Bucket Collection
+
+```js
+"buckets": {
+    "bucket": String, // index
+    "deleted": Boolean,
+    "permissions": String
+}
+```
+
+##### Object Collection
+
+```js
+"objects": {
+    "key": String, // index
+    "createdAt": Date,
+    "hosts[16]": [{
+    	"host": String,
+    	"disk": String,
+    }],
+    "deleted": Boolean
+}
+```
+
+```js
+"meta": {
+    "key": String, // index
+    "type": String // content-type
+    // type speific meta
+}
+```