[Auth] Reduce callback nesting (#15079)

Author: ncooke3

FirebaseAuth/CHANGELOG.md

@@ -10,6 +10,8 @@
 - [changed] **Breaking Change**: `TOTPSecret.openInOTPApp(withQRCodeURL:)` is
   now labeled with `@MainActor` and requires the `await` keyword when called
   off of the main actor or main thread.
+- [fixed] Simplified completion handler memory management in Auth interop
+  (#14962).
 
 # 11.15.0
 - [fixed] Fixed `Sendable` warnings introduced in the Xcode 26 beta. (#14996)

FirebaseAuth/Sources/Swift/Auth/Auth.swift

@@ -124,11 +124,12 @@ extension Auth: AuthInterop {
       }
       // Call back with current user token.
       currentUser
-        .internalGetToken(forceRefresh: forceRefresh, backend: strongSelf.backend) { token, error in
-          DispatchQueue.main.async {
-            callback(token, error)
-          }
-        }
+        .internalGetToken(
+          forceRefresh: forceRefresh,
+          backend: strongSelf.backend,
+          callback: callback,
+          callCallbackOnMain: true
+        )
     }
   }
 

FirebaseAuth/Sources/Swift/User/User.swift

@@ -1591,13 +1591,22 @@ extension User: NSSecureCoding {}
   /// on the  global work thread in the future.
   func internalGetToken(forceRefresh: Bool = false,
                         backend: AuthBackend,
-                        callback: @escaping (String?, Error?) -> Void) {
+                        callback: @escaping (String?, Error?) -> Void,
+                        callCallbackOnMain: Bool = false) {
     Task {
       do {
         let token = try await internalGetTokenAsync(forceRefresh: forceRefresh, backend: backend)
-        callback(token, nil)
+        if callCallbackOnMain {
+          Auth.wrapMainAsync(callback: callback, with: .success(token))
+        } else {
+          callback(token, nil)
+        }
       } catch {
-        callback(nil, error)
+        if callCallbackOnMain {
+          Auth.wrapMainAsync(callback: callback, with: .failure(error))
+        } else {
+          callback(nil, error)
+        }
       }
     }
   }