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.
UNDOCUMENTEDGetUserVotes
https://api.steampowered.com/IStoreSalesService/GetUserVotes/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
UNDOCUMENTEDGetVoteDefinitions
https://api.steampowered.com/IStoreSalesService/GetVoteDefinitions/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
string No
uint32 No
UNDOCUMENTEDPOSTSetVote
https://api.steampowered.com/IStoreSalesService/SetVote/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
int32 No
uint32 No
uint32 No
uint32 No