Add strict custom field registry

specs/versions/0.1/gsp.fields.schema.json

@@ -0,0 +1,57 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://gsp.local/schema/gsp.fields.schema.json",
+  "title": "GSP Fields",
+  "description": "Game Specification Protocol custom field registry schema.",
+  "type": "object",
+  "additionalProperties": true,
+  "required": ["gspFieldsVersion", "fields"],
+  "properties": {
+    "gspFieldsVersion": {
+      "type": "string",
+      "enum": ["0.1"]
+    },
+    "fields": {
+      "type": "object",
+      "additionalProperties": {
+        "type": "object",
+        "additionalProperties": true,
+        "required": ["type"],
+        "properties": {
+          "type": {
+            "type": "string",
+            "enum": ["string", "number", "integer", "boolean", "array", "object"]
+          },
+          "description": {
+            "type": "string"
+          },
+          "allowed": {
+            "type": "array"
+          },
+          "required": {
+            "type": "boolean"
+          },
+          "default": {},
+          "scope": {
+            "type": "object",
+            "additionalProperties": true,
+            "properties": {
+              "type": {
+                "type": "array",
+                "items": {
+                  "type": "string"
+                }
+              },
+              "idPrefix": {
+                "type": "array",
+                "items": {
+                  "type": "string"
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}