add: add ldap protobuf

proto/ldap.proto

@@ -0,0 +1,27 @@
+syntax = "proto3";
+
+package ldap_service;
+import "google/rpc/status.proto";
+
+service LdapAuth {
+    rpc VerifyUser (VerifyRequest) returns (VerifyResponse);
+}
+
+message VerifyRequest {
+  string username = 1;
+  string password = 2;
+}
+
+message VerifyResponse {
+  bool success = 1;
+  string error_message = 2;
+  UserData user = 3;
+}
+
+message UserData {
+  string dn = 1;
+  string display_name = 2;
+  repeated string groups = 3;
+  bool is_active = 4;
+}
+