Curve search bar Swift 4

i had problem to change my search bar design programatically on navigation controller. i just want to make the search bar curve like image below:

i had try a lot of example in stack overflow, but i still failed to change the shape. Here what it looks like now:

and here is the source code, on what have already done:

//MARK for searchBar UI
    searchController.dimsBackgroundDuringPresentation = false
    searchController.hidesNavigationBarDuringPresentation = false
    searchController.searchBar.placeholder = " Search for programs..."
    searchController.searchBar.sizeToFit()
    searchController.searchBar.isTranslucent = false
    searchController.searchBar.backgroundImage = UIImage()
    searchController.searchBar.delegate = self
    navigationItem.titleView = searchController.searchBar
    self.searchController.searchBar.layer.cornerRadius = 20.0
    self.searchController.searchBar.clipsToBounds = true
    // SearchBar text
    let textFieldInsideUISearchBar = searchController.searchBar.value(forKey: "searchField") as? UITextField
    textFieldInsideUISearchBar?.borderStyle = .roundedRect
    textFieldInsideUISearchBar?.font = textFieldInsideUISearchBar?.font?.withSize(14)

and now, i really have no idea how to change it, thanks in advance.

This will help you,

let searchBar = UISearchBar()

On viewDidLoad()

searchBar.sizeToFit()
searchBar.placeholder = "Search"
self.navigationController?.navigationBar.barTintColor = UIColor.green //this is just for reference
self.navigationItem.titleView = searchBar

if let textfield = searchBar.value(forKey: "searchField") as? UITextField {
    textfield.textColor = UIColor.blue
    if let backgroundview = textfield.subviews.first {
        backgroundview.backgroundColor = UIColor.blue
        backgroundview.layer.cornerRadius = 20;
        backgroundview.clipsToBounds = true;
    }
}

Above code will give you following output,