protocol ConnectionServerProtocol {
    func connectWithUsernameAndPassword(username: String, password: String)
}

public class ConnectionServer: NSObject {
    var username: String?
    var password: String?
    let connectionServerProtocol: ConnectionServerProtocol

    public init(connectionServerProtocol: ConnectionServerProtocol) {
        self.connectionServerProtocol = connectionServerProtocol
    }
}

public func connectWithUsernameAndPassword(username: String, password: String) {

    self.username = username
    self.password = MD5(password)
    self.connectionServerProtocol.dataTask()
}

self.connectionServerProtocol.connectWithUsernameAndPassword(username:"someUserName", password: "SomePassword")

let cs = ConnectionServer()

let cs = ConnectionServer(connectionServerProtocol:ConnectionServerProtocol)

let cs = ConnectionServer(connectionServerProtocol: ConnectionServerProtocol.self as! ConnectionServerProtocol)

let cs = ConnectionServer.self
cs.connectWithUsernameAndPassword(username: SomeUserName", password:"SomePassword")

public class ConnectionServer: NSObject, ConnectionServerProtocol {
}

cs.connectWithUsernameAndPassword(username: SomeUserName", password:"SomePassword")