adds opja extension

extensions/2.x_official_extensions/opja.md

@@ -0,0 +1,49 @@
+### Open Private Join & Activation (OPJA)
+
+**Goal**:
+
+The goal is to support a protocol for sending [OPJA](https://iabtechlab.com/blog/wp-content/uploads/2023/06/Open-Private-Join-Activation_Version_1.011.pdf) encrypted matching labels using OpenRTB 2.x.
+
+**Requested Changes**:
+
+Addition to **User Extension** Object
+
+### Details
+
+Open Private Join & Activation (OPJA) is a protocol for enabling two parties to privately generate activation matches.
+OPJA uses advanced cryptographic techniques to keep private data securely encrypted throughout all steps of the process.
+Note, it is assumed that parties will collaborate with the appropriate regulatory agencies and vendor(s) to ensure compliance.
+
+A new field under `BidRequest->user->ext` is specified which is named `ojpa`. 
+It is an array of objects describing match jobs, each could be generated by one or more matching vendors.
+
+Below we describe each field within each match job object:
+
+| Key                 | Type             | Description                                 |
+| ------------------- | ---------------- | ------------------------------------------- |
+| name                | String           | The human readable name of the matching job |
+| matches             | Array of Objects | An array of objects containing encrypted matching labels |
+| matches[].id        | String           | The match transaction ID which is unique to each match job row |
+| matches[].el        | String           | The encrypted label which can be used to determine a match |
+
+Example Request
+
+```
+{
+  "user": {
+    "ext": {
+      "opja": [
+        {
+          "name": "matching-system-operator.com",
+          "matches": [
+            {
+              "id": "0x1234",
+              "el": "0x45668"
+            }
+          ]
+        }
+      ]
+    }
+  }
+}
+```