add docs

Sources/Realtime/V2/RealtimeClientV2.swift

@@ -365,9 +365,23 @@ public final class RealtimeClientV2: Sendable {
   }
 
   /// Sets the JWT access token used for channel subscription authorization and Realtime RLS.
-  /// - Parameter token: A JWT string.
-  public func setAuth(_ token: String?) async {
-    mutableState.withValue {
+  ///
+  /// If `token` is nil it will use the ``RealtimeClientOptions/accessToken`` callback function or the token set on the client.
+  ///
+  /// On callback used, it will set the value of the token internal to the client.
+  /// - Parameter token: A JWT string to override the token set on the client.
+  public func setAuth(_ token: String? = nil) async {
+    var token = token
+
+    if token == nil {
+      token = try? await options.accessToken?()
+    }
+
+    if token == nil {
+      token = mutableState.accessToken
+    }
+
+    mutableState.withValue { [token] in
       $0.accessToken = token
     }