feat(rpc): define auth protobuf package and Authentication model

buf.gen.yaml

@@ -1,19 +1,24 @@
 version: v1
 plugins:
+  # core apis
   - name: go
     out: rpc/flipt
     opt:
       - paths=source_relative
+    strategy: all
   - name: go-grpc
     out: rpc/flipt
     opt:
       - paths=source_relative
+    strategy: all
   - name: grpc-gateway
     out: rpc/flipt
     opt:
       - paths=source_relative
       - grpc_api_configuration=rpc/flipt/flipt.yaml
+    strategy: all
   - name: openapiv2
     out: swagger
     opt:
       - grpc_api_configuration=rpc/flipt/flipt.yaml
+    strategy: all

rpc/flipt/auth/auth.proto

@@ -0,0 +1,46 @@
+syntax = "proto3";
+
+import "google/protobuf/timestamp.proto";
+import "protoc-gen-openapiv2/options/annotations.proto";
+
+package flipt.auth;
+
+option go_package = "go.flipt.io/flipt/rpc/flipt/auth";
+
+option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_swagger) = {
+  info: {
+    title: "Flipt Authentication APIs";
+    version: "latest";
+    contact: {
+      name: "Flipt Team";
+      url: "https://github.com/flipt-io/flipt";
+      email: "[email protected]"
+    };
+    license: {
+      name: "MIT License";
+      url: "https://github.com/flipt-io/flipt/blob/main/rpc/flipt/LICENSE";
+    };
+  };
+  external_docs: {
+    url: "https://www.flipt.io/docs";
+    description: "Flipt Docs";
+  }
+  schemes: HTTP;
+  schemes: HTTPS;
+  consumes: "application/json";
+  produces: "application/json";
+};
+
+enum Method {
+  NONE = 0;
+  TOKEN = 1;
+}
+
+message Authentication {
+  string id = 1;
+  Method method = 2;
+  google.protobuf.Timestamp expires_at = 3;
+  google.protobuf.Timestamp created_at = 4;
+  google.protobuf.Timestamp updated_at = 5;
+  map<string, string> metadata = 6;
+}