My game authenticate player either by GooglePlayConnectRequest or DeviceAuthenticationRequest.
How can I know, for a given player, what's the authentication he used in Data Explorer?
E.g. Is player with DeviceAuthenticationRequest, he should has non-empty deviceRegIds? Otherwise he is authenticated by GooglePlayConnectRequest.
Note that a player CAN authenticate with both (for example) Device auth AND google play /apple game center auth.
Believe it or not, the player collection "userName" is indicative of the INITIAL auth method they use. If there is an ANDROID or IOS reference there, the player originally used device authentication. If instead, it shows something like "GY_XXXXXXX", then the player was originally created with Google Play authentication.
Regardless of what method (device auth or google/apple) the player was created with, the presence of entries in their externalAuthentications property is indicative of third party auth setups.
Note that deviceRegIds is only related to push notifications
best of luck!