Popping on All Flex radios.

I'm happy to provide info about the SmartLink system. First, you need to understand that the SmartLink service functions as a broker. It is a "middle man" to help facilitate a connection between a client (like SmartSDR for iOS) and your radio. In order to do that in a secure way, it needs to be able to perform authentication functions both for radios and clients.

Authentication (Auth0)

We use an authentication service called Auth0 to do authentication. This is actually what you are interacting with when you click to Log In to SmartLink. Once authenticated, Auth0 issues a token that can be passed along from the client to securely authenticate the user.

The Auth0 token verifies a radio's "owner." This is done by first logging into the account in the client, then associating that Auth0 user with a radio via the SmartLink registration process where you prove physical access to the radio.

SmartLink Server

The SmartLink Server exists as an internet service at smartlink.flexradio.com. As mentioned above, this server's purpose is to broker connections between a client and a radio. As such, it keeps track of radios that have been registered with SmartLink. Periodically (currently once every 30 seconds), a registered radio will send a "ping" to the SmartLink server as if to say, "I'm still powered up and running at this IP."

So when a client wants operate with SmartLink, it first obtains an Auth0 token. This is either recalled from a previous session or you get a new one by logging in. The client then makes a TLS connection to the SmartLink server and passes the token while asking for a list of radios associated with the token's user. This list is typically displayed in a radio selection window (we call this the Radio Chooser).

Connecting to a Radio

From there, when the client wants to connect to a particular radio, the client sends a message to the SmartLink server that it would like to connect along with detailed info about which radio and the clients current network info along with a unique session key. The SmartLink server can then relay this request to the radio to prepare it for the connection attempt given the current network info. Assuming that goes well (the radio responds as expected), the SmartLink server will respond to the original Client request that the Radio is ready and to begin the connection. The Client then attempts to connect to the radio directly via TLS and the original session key that was relayed through the server is sent from the radio to the client to ensure the security of this exchange. Once the session key has been verified, the client can have confidence of a secure connection to the radio brokered through the SmartLink server.

That's the high level nuts and bolts of the mechanics. There are a BUNCH more technical details of what happens in the actual connections that ensures that the TLS connection is handled appropriately. Feel free to ask questions and I'll do my best to answer them.