Add extraBody support

Sources/OpenAI/Private/Networking/Endpoint.swift

@@ -62,7 +62,7 @@ extension Endpoint {
     }
     request.httpMethod = method.rawValue
     if let params {
-      request.httpBody = try JSONEncoder().encode(params)
+      request.httpBody = try encodeWithExtraBody(params)
     }
     return request
   }
@@ -108,5 +108,33 @@ extension Endpoint {
     }
     return components
   }
+
+  /// Add extraBody handling through JSON merging
+  private func encodeWithExtraBody(_ params: Encodable) throws -> Data {
+    let encoder = JSONEncoder()
+    let baseData = try encoder.encode(params)
+
+    // Check if this is ChatCompletionParameters with extraBody
+    if let chatParams = params as? ChatCompletionParameters,
+       let extraBody = chatParams.extraBody,
+       !extraBody.isEmpty {
+
+      // Parse base JSON
+      guard var baseJSON = try JSONSerialization.jsonObject(with: baseData) as? [String: Any] else {
+        throw URLError(.cannotParseResponse)
+      }
+
+      // Merge extraBody into base JSON
+      for (key, value) in extraBody {
+        baseJSON[key] = value
+      }
+
+      // Re-encode merged JSON
+      return try JSONSerialization.data(withJSONObject: baseJSON)
+    }
+
+    // Return standard encoding if no extraBody
+    return baseData
+  }
 
 }

Sources/OpenAI/Public/Parameters/Chat/ChatCompletionParameters.swift

@@ -39,7 +39,8 @@ public struct ChatCompletionParameters: Encodable {
     temperature: Double? = nil,
     topProbability: Double? = nil,
     user: String? = nil,
-    streamOptions: StreamOptions? = nil)
+    streamOptions: StreamOptions? = nil,
+    extraBody: [String: Any]? = nil)
   {
     self.messages = messages
     self.model = model.value
@@ -69,6 +70,7 @@ public struct ChatCompletionParameters: Encodable {
     topP = topProbability
     self.user = user
     self.streamOptions = streamOptions
+    self.extraBody = extraBody
   }
 
   public struct Message: Encodable {
@@ -488,6 +490,9 @@ public struct ChatCompletionParameters: Encodable {
   /// A unique identifier representing your end-user, which can help OpenAI to monitor and detect abuse.
   /// [Learn more](https://platform.openai.com/docs/guides/safety-best-practices/end-user-ids).
   public var user: String?
+  /// Additional parameters that are not part of the standard OpenAI API but may be supported by the underlying service.
+  /// This allows access to experimental or provider-specific features.
+  public var extraBody: [String: Any]?
 
   enum CodingKeys: String, CodingKey {
     case messages