This page is just a reference of all the known Steam APIs, I do not know how they work. Please do not email me with questions.
UNDOCUMENTEDCancelPairing
https://api.steampowered.com/IRemoteClientService/CancelPairing/v1/
UNDOCUMENTEDCreateSession
https://api.steampowered.com/IRemoteClientService/CreateSession/v1/
UNDOCUMENTEDGetReplies
https://api.steampowered.com/IRemoteClientService/GetReplies/v1/
UNDOCUMENTEDPOSTNotifyRegisterStatusUpdate

Register for status updates with a Steam client

https://api.steampowered.com/IRemoteClientService/NotifyRegisterStatusUpdate/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
fixed64 No
fixed64 No
fixed64 No
UNDOCUMENTEDPOSTNotifyRemotePacket

Send a packet to a Steam client

https://api.steampowered.com/IRemoteClientService/NotifyRemotePacket/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
fixed64 No
fixed64 No
bytes No
UNDOCUMENTEDPOSTNotifyUnregisterStatusUpdate

Unregister for status updates with a Steam client

https://api.steampowered.com/IRemoteClientService/NotifyUnregisterStatusUpdate/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
fixed64 No
fixed64 No
UNDOCUMENTEDSetPairingInfo
https://api.steampowered.com/IRemoteClientService/SetPairingInfo/v1/
UNDOCUMENTEDStartPairing
https://api.steampowered.com/IRemoteClientService/StartPairing/v1/