feat: static json credentials (#2423)

internal/proto/controller/api/resources/credentials/v1/credential.proto

@@ -69,6 +69,11 @@ message Credential {
       (custom_options.v1.generate_sdk_option) = true,
       (custom_options.v1.subtype) = "ssh_private_key"
     ];
+    JsonAttributes json_attributes = 103 [
+      (google.api.field_visibility).restriction = "INTERNAL",
+      (custom_options.v1.generate_sdk_option) = true,
+      (custom_options.v1.subtype) = "json"
+    ];
   }
 
   // Output only. The available actions on this resource for this user.
@@ -155,3 +160,25 @@ message SshPrivateKeyAttributes {
     }
   ]; // @gotags: `class:"public"`
 }
+
+// The attributes of a JSON Credential.
+message JsonAttributes {
+  // Input only. The secret associated with the credential.
+  google.protobuf.Struct object = 10 [
+    json_name = "object",
+    (custom_options.v1.generate_sdk_option) = true,
+    (custom_options.v1.mask_mapping) = {
+      this: "attributes.object"
+      that: "Object"
+    }
+  ]; // @gotags: `class:"secret"`
+
+  // Output only. The hmac value of the object.
+  string object_hmac = 20 [
+    json_name = "object_hmac",
+    (custom_options.v1.mask_mapping) = {
+      this: "attributes.object_hmac"
+      that: "ObjectHmac"
+    }
+  ]; // @gotags: `class:"public"`
+}