Android :: PHP Socket Server (Push Notifications) - Security / Authentication

I have recently written a socket server in PHP that will be handling communication between an Android phone application and my PHP webserver. Due to the fact that Android doesn't natively support push style notifications we are going to be using our webserver as the middleware layer to handle our 'pushes'. The socket server is stable, runs well, and seems to scale nicely. While I would eventually like to re-write this in C I don't have the skill necessary to do that right now so I am going to be staying in PHP for at least a short while. As of this moment our Android emulator is able to communicate through the server, get pushes, etc. so that part is all covered.

My concern is that, right now, anyone can open a socket to my server and will be given a client connection. While we won't be passing sensitive data back and forth I don't want to allow just anyone to connect over and receive broadcast information, eat up my resources, and clog my server in general. The question is, how do I secure a server like this? Let's assume that I am running on port 25,000--can I set up some sort of SSL layer on that port and expect devices like the Android to be able to communicate over that port without any special protocols or jumping through hoops? I have considered asking the connecting clients to authenticate their user against our user database before being given a client connection, but that would require the passing of credentials in plain text over the network which I am not about to do.

I am rather new to straight TCP communication from PHP and feel like I might just be missing something simple that allows for authentication on this level.
Additional information: If I am able to get a valid username and password securely I would be using MySQL to validate the user and then accept/reject their connection based on the results of the query.