Правильное использование статьи раздела и заголовка

swift 4:

let username = "username"
let password = "password"
let loginString = "\(username):\(password)"

guard let loginData = loginString.data(using: String.Encoding.utf8) else {
    return
}
let base64LoginString = loginData.base64EncodedString()

request.httpMethod = "GET"
request.setValue("Basic \(base64LoginString)", forHTTPHeaderField: "Authorization")