About Steam Friends API
Developer API used to check a player's Steam friends 
Disclaimer
This plugin checks from both players Steam profiles if both players have a private profile, then it will return false, even if they are Steam friends.
On it's own this plugin does nothing, it's meant to be used by other plugin developers as a dependency.
Use Cases
The API could be used to automate team / clan / teleport request / door auth / turret auth if steam friends, could also be used to determine if players may have a secret alliance, easily find out if a player is friends with a cheater etc...
Configuration
"SteamAPIKey":Steam API key (get one here https://steamcommunity.com/dev/apikey)
"initDelay":Delay between Steam query during plugin load event, min = 1 max = 10, default is 1 second
"refreshInterval":Minimum time before a user's friend list can be updated, min = 60 max = 86400, default is 3600 seconds
Developer API
(bool)isSteamFriend(ulong steamID, ulong targetSteamID) // Returns true if input(steamID and targetSteamID) are Steam friends (List)<BasePlayer>inGameSteamFriends(ulong steamID) // Returns a list of online in game players of which are steam friends with the input(steamID)