Auth (#1147)

Implement the Auth interface, with JWT and service implementations.

* Update Auth Interface

* Define Auth Service Implementation

* Support Service Auth

* Add Auth Service Proto

* Remove erronious files

* Implement Auth Service Package

* Update Auth Interface

* Update Auth Interface. Add Validate, remove Add/Remove roles

* Make Revoke interface more explicit

* Refactor serializing and deserializing service accounts

* Fix srv name & update interface to be more explicit

* Require jwt public key for auth

* Rename Variables (Resource.ID => Resource.Name & ServiceAccount => Account)

* Implement JWT Auth Package

* Remove parent, add ID

* Update auth imports to v2. Add String() to auth interface

auth/service/proto/auth.proto

@@ -0,0 +1,50 @@
+syntax = "proto3";
+
+package go.micro.auth;
+
+service Auth {
+    rpc Generate(GenerateRequest) returns (GenerateResponse) {};
+    rpc Validate(ValidateRequest) returns (ValidateResponse) {};
+    rpc Revoke(RevokeRequest)  returns (RevokeResponse) {};
+}
+
+message Account{
+    string id = 1;
+    string token = 2;
+    int64 created = 3;
+    int64 expiry = 4;
+    repeated Role roles = 5;
+	map<string, string> metadata = 6;
+}
+
+message Role {
+    string name = 1;
+    Resource resource = 2;
+}
+
+message Resource{
+    string name = 1;
+    string type = 2;
+}
+
+message GenerateRequest {
+    Account account = 1;
+}
+
+message GenerateResponse {
+    Account account = 1;
+}
+
+message ValidateRequest {
+    string token = 1;
+}
+
+message ValidateResponse {
+    Account account = 1;
+}
+
+message RevokeRequest {
+    string token = 1;
+}
+
+message RevokeResponse {}