feat(smauth): Add steam login

smauth/smauth.gd

@@ -63,7 +63,45 @@ func login_device_auto():
 	cfg.save(file)
 	return login_device(cfg.get_value(section, "device_id"), cfg.get_value(section, "device_key"))
 
-
+## Login using a Steam auth token.
+##
+## This only work if steam login provider is enabled in the backend.
+##
+## [param identity] The identity used to generate the auth token. This can be
+## any value that would identify your service/game.
+##
+## [param ticket] The hexadecimal-encoded binary of the authentication ticket returned
+## by Steam's GetAuthTicketForWebApi SDK function.
+## See https://partner.steamgames.com/doc/api/ISteamUser#GetAuthTicketForWebApi.
+##
+## Example usage with GodotSteam (https://godotsteam.com/).
+## [codeblock]
+## # Request a web API ticket.
+## var identity = "my_godot_game"
+## var ticket_id = Steam.getAuthTicketForWebApi(identity)
+## assert(ticket_id != 0)
+##
+## # Get the ticket for the response.
+## var res
+## var res_ticket_id = 0
+## while res_ticket_id != ticket_id:
+## 	res = await Steam.get_ticket_for_web_api
+## 	res_ticket_id = res[0]
+## assert(res[1] == 1) # Check if request was successful (result = 1).
+##
+## var ticket_buffer = res[3]
+##
+## # Login using token.
+## var response = await W4GD.auth.login_steam(identity, (ticket_buffer as PackedByteArray).hex_encode()).async()
+## [/codeblock]
+##
+## Note: setting up GodotSteam requires more than this code snippet (some configuration
+## and callbacks setup). Check out https://godotsteam.com/tutorials/initializing/ and
+## https://godotsteam.com/tutorials/authentication/ for more information.
+##
+## Note: while GodotSteam is not a strict requirement for using this login method, a
+## way to access the Steam SDK within Godot is required. Right now, GodotSteam is the
+## easiest way to achieve this, so its usage is very recommanded.
 func login_steam(identity: String, ticket: String):
 	return begin_sso(
 		"anon.localhost"