I don't know if it's possible, but it would be nice to have ability to check and validate the format of the device registration token before we pass to the server.
Why are you worried about validating the token? You should be always getting it from the InstanceID library on the client, hence it should always be valid.
I don't know if it's possible, but it would be nice to have ability to check and validate the format of the device registration token before we pass to the server.